Live poker I don't typically eat or drink while playing to prevent giving off
tells, but if I did eat (between hands etc.), then something easy to eat without a mess.
Health bars, or anything bite-sized are good choices.
For
online poker, there is a little more freedom (not only due to lack of physical tells, but mostly because you can pretty much have whatever if it fits near your computer space).
For online poker, usually just a cup of coffee is all I need