Even factoring in the cost of groceries, I averaged about $80-100 savings per trip by bringing my food. So depending on how many trips a month you fly, you could easily save in the range of $400. And one could probably do even better than I did by shopping at Costco and buying in bulk.

To answer the OP's question, I always carried 3 bags - 22" luggage, flight case, and cooler. That said, if you're at a carrier that uses EFBs, I'd definitely consider a combo EFB flight bag/cooler. 3 bags makes commuting or deadheading a pain.