When I sleep I just usually sleep on the road. I have never really had much difficulty when dangerous animals ambush be in my sleep, I just get up and chop them in two. Then again I've never been ambushed in my sleep by anything bigger than a cougar, I have some megabeast size crap wandering around as wildlife, getting ambushed by one of those could probably make the nap permanent quite fast. Maybe I should start hiding before I sleep.
To solve the water problem I usually try to carry around more than 1 waterskin. When I'm doing a no T challenge I'm often carrying 4 or more full waterskins. Food I also carry extra of, but usually no more than 10 units, indeed it is rather easy to find vermin, and if you are going on a long trip you can stockpile and store them just like food. Pixies are my vermin of choice. I imagine them refilling my hearts every time, just like in Link.
(...What you thought they just restored his health and flew away? Ha! They have been stolen from their friends and families with some big net soaked with insect parts, locked in an airtight glass bottle that smells like rancid Lon Lon milk with a long dead bee in one corner, in some obscure pocket in link's tunic for lord knows how long. They most certainly would not be friendly after that, if even still breathing. You never saw them fly away after he grabbed them in the original link did you, DID YOU? They just decided they needed to be a bit more PC as of late in regards to the fairies.)