We often plan for leftovers of pre-cook foods when planning our meals. And we sent 5 kids off to college with precooked food so we had lots of practice. Now, with just two of us and our lids living hours away, make ahead meals allow us to cook stuff the would be awkward with just the two of us. A whole turkey or packer brisket and just two people can be more like a sentence than a pleasure if you don't have a way to save some for later.
Depending what he has to cook with make ahead meals can be heated up in the bag in a pan of water, on a stove top, in a microwave oven and a standard oven, toaster oven or air fryer work great to heat and crisp things up. Not knowing what he has to cook with and how willing he is to do more than heat and eat some of this may not help but....
If you want to vacuum seal ribs or other items with exposed bone go online and order a pack of vacuum bone guards-thick sheets of plastic to shield the sharp edges of bone and protect your bag. I just order some on
Amazon....
If he has access to a vacuum sealer at school small stuff like meatballs, small fruits etc can be frozen on a sheet pan, vacuum sealed at home to be opened at school, take out what he wants and reseal.
Pork butts can be turned into pulled pork, sliced smoked pork or oven roasted pork slices and all reheat great.
Poultry done anyway that doesn't dry it out works well. If I'm smoking one or more turkeys I usually pick up some extra wings and giblets and some aromatics, cut it all into chunks, spray them with cooking spray and roast it all at high temperature stirring often until browned. I then make concentrated stock for a gravy base and put a small bag into each package of meat. That way if we want gravy we only need to heat and thicken the gravy base. Maybe one day I'll experiment with tapioca starch or arrowroot as thickeners as they are supposed to be the thickeners to freeze and thaw the best and make the gravy ahead.
Don't think I'm nuts but you can grill a steak to rare or medium rare, let it cool and seal it. To reheat he can use about 30-50% microwave power and even brown it in a hot skillet of on a grill. If done in the microwave alone it won't have any of the crust remaining but it'll still be a rare steak....
We have a chamber vacuum sealer so while we can take liquids right to the vacuum sealer and seal them you might need to take an extra step with wet food or liquids. For example you can freeze soup or stew in a vacuum bag that is laying flat on a sheet pan with the open end of the bag up on the rim of the pan and seal it after it is solid. R freeze liquids in a tray, pop them out and seal. Smaller quantities of liquids (like gravy or sauce) can be frozen in ice cube trays before sealing and that also makes portioning easy.
Even if your sealer has a "Seal" button that you can push at any time, items prone to being deformed in vacuum sealing benefit from being frozen to at least what the food industry calls the "frost crust" stage before sealing. Meatloaf, lasagna portion etc all seal just fine that way but it's important to have him cut the bag while they are still frozen of the vacuum will crush the food.
OK, enough of my rambling for now.... Have a great weekend.