What do you meal prep?

All of these photos that everyone posts here are very great and all, but they specifically are for those who are trying to lose weight. I don't want to lose weight. I want to gain weight. What should I meal prep for that? I have a very busy schedule and it's always hard for me to eat and I usually end up just eating like half of a granola bar or something because I have like no time to eat. A friend recommended to me meal prepping, but I don't want to lose weight so what should I prep? Should I just like mix up a bunch of wet ingredients from a recipe, put it in a container and take it with me? I am very confused about meal prepping. What are my options? Please inform me about meal prepping because I want to start doing this.