IME the snacks are self serve, but FAs might not be happy about you helping yourself to the alcohol or carrying a hot cup of coffee back to your seat. In general, ti's better to ask for the beverages, either by finding a FA in the galley or by ringing your call button. Better yet is to flag down a FA walking past your seat, but this can require a long wait and this isn't a reasonable expectation for the customer's behavior.