Must try "maizes zupa", which is a bread dessert or "maizes kartojums". That's very Latvian. Otherwise, food is very similar to German cuisine as well as influenced by the USSR.
Try cheese with caraway seeds, again, very Latvian.
Black balsams - traditional herbal drink. I prefer one with currents and they sell those in tiny bottles, so it makes it easy to try.
Try a drink called "Kvass". It is non-alcoholic. You might like it.
Pork dishes are very popular and according to my meat-eater friends, taste amazing.