DIY Solar Water Still. Make your own distilled water from stream or lake water, salt water, or even brackish, dirty water, using these DIY Solar Still plans
I'm not a fan of canned food but in a pinch it is better than nothing.
If the SHTF, antibiotics will be scarce, which means many people could die from minor infections. Learn to make your own antibiotics. - I'm allergic to penicillin but my children aren't so this is definitely going in my book