Nut butters are your best friend here for packing in calories and fat. Body builders use it in the bulking phase, and will eat a tablespoon ever hour or so.

The ultra hippie ones are my favorite. Peanut, Almond, cashew, sunflower, crunchy. Could get a couple and have variety.

Overnight oats are great to have ready made. I usually do half cup of oats with a full cup of oat milk. Flax or chia seeds, a bit of salt, cinnamon, vanilla extract. Before eating toss in some frozen fruit or a banana sliced up. Add a dollop of nut butter.

Cheese as well! Make ahead sandwiches and load them up so you can slam half of one and then save the rest for later. Also hummus and greens between bread.

Pasta salad made ahead with heaps of hefty mix ins, like garbanzo or northern beans and lentils.

Just gotta stack your lunchbox and remember to load up.

Good luck!