**Quark: adds and changes a lot of things that make the overall vanilla experience much better—it’s very configurable
Hopper Ducts: adds simple ducts that can transport items from hoppers to another inventory like normal hoppers, except they also work upwards
Inventory Tweaks: adds ways to sort your inventory and conveniently move items to other inventories, as well as other features such as features that replaces weapons and tools before or after they break, replaces blocks when you’ve run out of a stack, and more
Convenient Recipes: adds more recipes for vanilla items) (not for 1.10 or 1.11)
OptiFine (optimizes your game to improve your frame rate, adds lots of options so you can customize graphics, performance, etc., adds support for shader mods, and more (you are not allowed to put it in modpacks, but you should recommend that people install it, because, well, it optimizes the game and is useful for nearly everyone)
Portable Craft Bench (or Portable Crafter, if you want a few more options and a more expensive recipe): adds a crafting table which you don’t have to place to use
Bow Infinity Fix: makes it so that you don’t need an arrow in your inventory to use a bow with the Infinity enchantment (not for 1.9, 1.10, or 1.11)
DrCyano’s Lootable Bodies: adds inventories to corpses and replaces the vanilla drop system for mobs
Storage Drawers: adds several drawers that hold several stacks of one type of item and drawers that can store several stacks of two types of items, as well as several upgrades, such as upgrades that increase the amount of stacks each drawer can hold
Chisel: adds a few new randomly-generating blocks as well as a tool that can change the appearance of almost every vanilla block
Just Enough Items: allows you to see the recipes and uses of every single item and block in the game
Iron Chests: adds various different chests following the tier system of vanilla Minecraft
Carpenter’s Blocks: allows you to change the appearance of many blocks to truly customize your builds (there is no stable version for 1.10 or 1.11 yet, however)
HWYLA: tells you whatever block, mob, or plant you’re looking at and what mod it’s from
Waila Harvestability: an add-on for HWYLA that tells you if you can safely break a block or plant and what tool you need to break it or the recommended tool to break it (such as an axe for logs and a shovel for sand)
Debatable
Natura: adds lots of naturally-occuring trees, mobs, bushes, and more (maybe too much variety to be vanilla-like?)
Biomes o’ Plenty: adds tons of biomes, plants, and more (again, may be too different and add too much to be vanilla-like; also causes frame rate issues on low-end computers)
JourneyMap: a minimap mod that supports mob-, player-, and cave-system-viewing—also has a feature that lets you save waypoints
BiblioCraft: adds tons of items for storage and decoration (adds so many, many of which differ quite a bit from vanilla Minecraft, however)