Few trains serve food at your seat NOW (I didn’t see mini-bars in operation when I visited SW in late Aug.), the Glacier Express did serve hot food (in First Class only(?)). Pre-Covid the food on the GE (IMHO) didn’t seem that “exciting” and was expensive.
I assume the MIGROS/COOP dining (=picnic) option would still be OK while riding trains (not require a COVID test).