This is obviously biased but it is my own mod, "TheMasterCaver's World", which is sort of like Biomes O' Plenty (in fact, one time somebody even thought that was what I was using) and much more.
Aside from that, the only mod that I regularly use which is not my own is Optifine; the last time I used any other mods besides my own was several years ago, which included Backpacks, Rei's Minimap (this shows the age, as the original creator discontinued it after 1.6.2), an amethyst armor/tools mod plus my own mini-mod which hacked in an ore (I used MCreator to make a simple Forge mod which dropped the item ID used for amethyst, something which is only possible in versions which use numerical IDs, which was otherwise crafted out of quartz and other materials), and Improved First Person View.
Yeah, that guy in the avatar is me. I'm *that* strange. It happens. Sometimes people act like that. Just go with it. I can offer help with suggestions even before you post them - NOT make your suggestions - but help you with them.
Iron Backpacks. Once you learn how to configure them, you won't be able to play a pack without them.
I can make a backpack that picks up ores, destroys cobble and refills my food/potions for when I go mining. I could also make a backpack that picks up any crops I get when harvesting my farms and keeps a stack of each type of seed on my hotbar to replant.