We love to hit the lounges for lunches. Love Nomad's Lounge at AK, Cava del Tequila for guac and salsas and margaritas in Epcot, HBD Lounge at DHS, Ale and Compass lounge, if you are near Yacht Club. We love that we don't have to plan in advance and can choose when and where to go depending on how we feel that day.
For QS, we like Satuli in AK, Tangerine in Epcot, BoG at MK (haven't been there since they changed the pork to chicken though, not sure if I would still recommend it!).
For TS, we like Skipper's at MK, Sanaa at AKL, and HBD or 50's at DHS.
Nothing is really a must do for us though.