Unless players can access your pockets in MP, this is one of those "issues" that has a built in solution, if it bothers you, don't do it. Changing armor should be a no no, changing equipped weapons as well, excepting weapon swapping, but the simplest solution to "I don't like that I can take stuff from other characters in my party" is to not do it. I seriously did not know you could eat food during combat, because it never occurred to me to try, just like I never thought of taking items from another character during combat., or taking a long rest after every fight. It's just things that were a non issue for me, because I didn't do it, or didn't know you could.
