You must declare all food products. Failure to declare food products can result in up to $10,000 in fines and penalties.
The following are generally admissible:
(...)
-Coffee - roasted or unroasted if there is no pulp attached.
Portanto, não deve haver nenhum problema com as cápsulas de café, desde que elas sejam para seu uso pessoal, mas você precisa declará-las.