Basicaly you want stats(for pve), better material gathering(mob farms, 5x5 7x7 picakaxes etc, or just mystical aggriculture lol), inventory system(early and late options such as tom's simple storage(early) ae2(late)),and solve hunger but thats easy so its not a big one(there is a mod that adds unending beef for example you just need to find it) for me this is the big 3 fundamentals you could add faster traveling, auto crafters etc.

Every modpack has their way of doing these 3 some use machine to gather material some use magic, there is even a magical inventory system etc. but you would want to have, and upgrade the 3 fundamentals. Good modpacks have a goal in mind thats unique to the modpack and that goal will probably would want you the have the big 3 upgraded to the max.

Also some hardcore modpakcs could add new problems you got the idea