Tucking in to a meal is the marmoset familys favorite pastime.
We make sure they have plenty of highly nutritious foods. Zupreem Marmoset food is our marmosets staple diet, we add fresh vegetables - NEVER, NEVER ONIONS - Fresh fruits, they also love nuts (almonds, walnuts) never give them raisins.
They do need Vitamin C, so a mandarin orange sliced up small.
Remember to be careful, and do your research, this is just a small sample of what we feed ours. I try to change it up continuously, but always check that it is actually safe to give to marmosets before introducing something new. There is also Marmoset biscuits, hard little biscuits, specifically for marmosets. Canned and packaged marmoset food is available on Amazon.