Replying to I need advice for starting to work out.

I am going to a rigorous backpacking camp in about 4 or 5 weeks. I need to start getting I shape for it. I don't work out and I need to start. The camp will involve white water rafting, rock climbing and backpacking. We will be carrying a large, heavy backpack for all 3 weeks of it. Anyone who's a health nut.. Can you help me get an idea of what excersise I should start to do? Also, if anyone is looking for a challenge.. I am not going to be able to refrain from fapping for 21 days. Devise me a clever plan to stealthily fap in the forests of Oregon? +k if you guys genuinely help me out. Thanks!