You can say any of the four and sound completely natural. We use them interchangeably.

I'd personally use 'can I have' and 'can I get' to ask for food, because these can be made into interrogatives. Examples: Can I have the pie please? Can I get some chips too? You can also use 'I'll have', but this is more of a statement. Example: I'll have the chicken please. I'd avoid 'let me get', because it may be seen as too direct (in Britain anyway)!

Thank you Brian. Actually, I hear "let me get" often here in Texas. It might be a cultural thing. I don't like to use it though. I usually say "Can I have" or "I'll have".

Hello Fernando, you could also say 'Could I have' or 'I would like'. I have never heard anyone saying 'Let me get' in this context. Regards. Brian