The use of でも and ででも in this sentence

Question

A: あ……えっと……何か手伝うことは、ありますか？

B: ん？　あぁ、この辺はドシロウトにできるこっちゃないからな。　邪魔にならねぇように先にメシでも食って、後は舞台袖ででも大人しくしてな

Pretty much in general でも and ても don't sit well in my mind. There have been a lot of times I see them in a context in which they don't make sense to me as "even" or "even if/though" or in the case of でも as で and も individually. In this case the manner of speech is colloquial so maybe that's why it seems so odd. What really confuses me is ででも. Can someone explain the use でも and ででも here?

As a bonus, is にならねぇ just にならない with a a different emphasis?

Answer 1

This でも means "〜 or something similar". So メシでも食べて means "eat some rice or something". The ででも in question is just the action-location-marker で plus the previous でも. So 舞台袖ででも大人しくして means "wait/behave quietly in the 舞台袖 (or somewhere)".

(Not sure of the best translation for 舞台袖 -- literally the "wings of the stage", but maybe something like "off-stage" or "off to the side of the stage" might be better).

Bonus: Yes, your intuition is correct. 〜ない often becomes 〜ねぇ in very casual speech.