Spring rolls wrapped in either rice or vegetable wrappers (veggie wrappers could be thinly sliced zucchini or daikon, lightly steamed cabbage or chard, Romaine or Boston lettuce ... )
Hummus with gluten-free crackers (homemade or storebought)
If they eat meat, seafood and/or dairy your options are just about unlimited ...
Deviled eggs
Any toothpicky meat/fish/shrimp/sausage thing
Cheese cubes with quince paste and/or or a selection of fancy honey
...