I have been re-using a mask when I've been out. We take large Ikea food bags which is sturdy plastic with a zip seal. When I have finished with my mask for now, I fold it in half (I understand some styles may not be easy to fold) so the "contaminated" part is on the outside, then it goes straight into the food bag, doesn't even touch the sides and is sealed. When I need it again, it comes straight out, holding the ear loops. I don't know how else to keep a used face mask.
Adjusting the face mask with clean hands only, I touch either under the chin, the bridge of my nose or just where it sits on my cheeks.
I think a full day out somewhere where you are going to get hot and sweaty, maybe it's raining etc, would require more than one mask. I think for most people as long as you put it on properly and take it off correctly, one mask should be OK.
But I guess having a spare one is a good idea.
As to eating a drinking, currently, we have only been eating in the car so no mask, but when outside with a mask and needing a drink, I unlooped one ear, keep hold of the loop with one hand, and drink with the other.
My brother did make a stupid comment the first day we wore face masks outside - basically why take a drink out with us because we can't drink while we have the face masks on.
(that wasn't quite my expression, more disbelief that we share the same genes)