Pickles and lard. Perfect with alcohol.
Grandma's pickles and lard are one and the same quest item. If Geralt invites Zoltan to be his guest at Shani's party, the dwarf gets a hankering for some food and asks the witcher to sneak downstairs and get some pickles and lard from Grandma's larder downstairs. He says Geralt should do it as dwarves are no masters of stealth.
Zoltan is, hands down, the best of the three possible party guests, but you should not miss out on some more fun by not exploring the other two options.