Can i use "to" instead of "ya"?
あめ と おかし。 candies and treats only. just candies and treats.
あめ や おかし。 candies and treats etc. candies and treats and something.
very useful to know, ありがとう!
You'd use と if you're giving an exhaustive list; you'd use や if you're just giving some examples from a larger list.
と implies that you are exhaustively listing everything. So it's not really appropriate.
Yes you can. The meaning has a small difference.
In casual language is it possible to leave out the が before the すき? It feels like it flows better without it.