If you burn things…well, I just take the ash outside and dump it on the lilacs. They like the lime and potash.In any other case, if you burn something just chuck the ash.
As for food…offer it, and then it’s fine to eat it yourself if you want. Cultures have done THAT for thousands of years. Same for drink. The gods take the ‘spirit’ of it. You take the mortal remains into yourself. You can let it sit on an altar if you wish, and then eventually throw it away, but I don’t like wasting food that way personally.
Odin, in particular, has a rather strong reaction to offering to pour out some whisky to him, with that reaction being “NO DO NOT WASTE THAT THAT IS GOOD WHISKEY DRINK IT FOR MY SAKE.”
