I've never actually done it myself, though I've read quite a deal on the topic of long backpacking trips, and have been trying to get out on a week-long one here for a while now (like, 2 years). I've taken a number of 2-3 day trips, however. So, I'll offer what knowledge I've gained, and hopefully it'll be useful.
First (this is very important!): a 7-day hike off in the "woods" is foolish if you're not informed on what you're getting into; it's also not the wisest idea for an amateur long-distance hiker to over-estimate his or her own ability and go solo until you've got a couple trips under your belt.
Second (as has been stated several times already): 70lb is way, way too heavy. Period. Think half that weight, or maybe a little more, in food. The tools and supplies you need should fit in under 35lb without a problem. This is all off the top of my head what I would do for a 7 day hike:
- backpacking stove (some places disallow fires) and fuel - 3lb (I like the duel fuel variety - much lighter than propane for long-term/with a lot of fuel)
- single, lightweight/aluminum pot - 6oz-8oz
- water purification tablets/kit - 1lb
- First-aid kit - ~1.5lb (don't skimp here!)
- sleeping bag - 3lb max unless you need 3-season
- sleeping roll - 8oz
- backpacking tent - 3lb
- 1 change of clothes for weather expected (2lb)
- long clothing for inclement weather/mornings and/or a lightweight jacket or vest, warm hat/gloves (3-4lb) (of course this would all depend on where and when you're going and how high you're climbing - most I'd likely ever want would be a fleece at a couple ounces)
- three pairs of good wool/poly blend socks and underwear (wash and rotate, drying throughout the day with 1 in reserve - dry clothing makes a lot of difference in energy levels if the temp drops at all, and that can be dangerous)
- poncho to go over you and your gear that can double as a canopy/tent: 10oz
- utility knife, wire saw (x2), fire kindling, emergency whistle, "fishing equipment", maps, compass, one or two heavy ziplocks, trash bags, LED flashlight: about 2lb
I'm sure I'm forgetting something or mis-stating the weight of something, but that's about 28lb in gear and most of what you should have with you, and you could probably use that weight limit and add a couple other things, if you've got really light-weight gear - or carve off more weight still. That leaves 7lb for 7 days (dried food doubles in weight or more when re-hydrated), which would be a bit conservative for something energy-intensive. I'd feel comfortable going up to 45lb total in food, depending on how much you need to eat to stay going.
But keep in mind that the recommended MAX weight of a pack for long-term hiking, even if you've got a really good pack, is about 1/4th your fit weight. If you're out of shape and fat, that number is going to be lower. For instance, my fit weight is 170, but I'm not fit and still weigh that much; therefore, the max I should carry would be around 40lb, or 160/4.
Keep in mind that food will be your main concern on such a trip: if you're 3 days out and you've already eaten 3/4ths of your food, you will need to turn back. While a person can survive at length without nourishment, there is a period of time initially after intake where a person will be particularly vulnerable to sickness due to the increased stress and the change in metabolic process, and your energy levels will be almost negligible until you get used to metabolizing fat (and then soon afterwards, muscle and connective tissue). So: don't let yourself get too hungry; and assume you'll eat three or four times as much per day as you would on your average day. Basically, every day is Thanksgiving - though that does depend on how much gear you're hauling, and how hard you're pushing yourself as well.
Re: dehydrated foods: the dehydrated foods you typically buy at the grocery will have sulfates added to them in high quantities for the purpose of preserving the food. Unfortunately, that will (in short order) make your body quite acidic; you will get (bad) heart burn, muscle cramps and maybe rashes unless you do something to mitigate the problem. You could also dehydrate your own food and reconstitute it, or simply get unsulfated foods to help mitigate the problem.
Also, dehydrated foods will generally reconstitute to twice to three times their dehydrated weight for commercially available dehydrated foods. This also means you'll need to drink water while you're eating the dried foods in order to not get dehydrated and constipated; a sip for every nibble, a slurp for every bite.
Health food stores often seem to have dehydrated fruits and veggies which are good for backpacking - either in eating as-is (make sure you gnaw on 'em quite a bit before swallowing to make sure they'll digest completely and you get all their benefit) or to reconstitute in your pot with some water. (Also, a neat trick is to put the food you're going to cook/reconstitute in a ziplock with some water and put it on top of your pack or in the top pocket of your pack an hour or two before you plan to eat: the sun from the day will start tenderizing/rehydrating the food so you don't have to waste as much fuel on it.
The foods you will want to bring should have a moderate salt content, because you'll be breaking your muscles and body down through exercise, you'll be sweating, etc. and you'll need salt. Fat and protein will be essential, so a pound of nuts (trailmix) is suggested in addition to any jerkied meats. You'll also want carbohydrates, so either bring something like an unleavened bread, hardtac (I can't stand that stuff), or something like rice or oatmeal. If you've currently got a high-sugar diet (drink any soda? eat crispy poof cereals for breakfast? etc.) then you're going to probably want to bring some along as well, because you will crash and crave the stuff - though it'd be better to cut it from your diet beforehand so you get used to a lower sugar diet. You'd be surprised how sugar withdraw can make you cranky and sluggish.
Jerkied meats shouldn't be the store-bought variety, either. They don't dehydrate their meats enough, and in reality half of what you're eating is just caramelized flavoring anyway in some cases, unfortunately (used to work at a jerky plant - pretty disgusting). Making jerky is easy and reasonably inexpensive. You can turn 4lb of meat into about 2lb of jerky over night in the oven, if you make your own meat hangers to hold all the meat (coat hangers and screen door
Anyway, I've gone on long enough. Hope that's useful. Now for the question that's being asked: I'd recommend a lightweight revolver in .357 mag with good ammo and maybe an extra clip. Chances are you won't have to use it, but if you have to, you'll want it (ie a cougar - which is actually another argument to not go on such expeditions alone, and the main reason I haven't done so: it's dangerous). Of course, you should comply with all regulatory laws and all that too. And it appears you're not allowed firearms where you're going - so don't be foolish and go it alone. (Two people: you may be able to scare off the cat or fight it off and get help. One person: you're dinner, even if you have a gun - they'll just take you from behind like they normally do.)
The primary point I hope you take away from all this is that the firearm is secondary to good planning and preparedness in other things. Same goes for SHTF preparedness: all the ammo in the world won't save you if you've only got half a dozen cans of beans and a couple packets of ramen.