A side activity would be anything outside of the main combat loop. Things like collectibles, crafting mechanics, etc.
I don't know what the consensus is about these, so i propose a few to discuss about.
Alchemy
Players can find various materials by killing enemies, random loot or from merchants.
These may have a certain properties that when mixed, are added togheter to a single potion. This allows players to mix several potion effects into a single one. Players may save potion presets for quicker crafting.
Some more niche effects may be exclusive to player made potions or it may allow players to have more buffs than it would be otherwise possible with store-bought potions.
The amount of effects and their intensity contribute to a "potency" value, players can withstand a certain amount of "potency" at any given time. This potency wears off with the potion's effects.
Enchantments
Players can have an enchantment in each piece of equipment. Most enchantments have drawbacks and are meant to reinforce builds.
Most drawbacks are about stat shifting, rising one while lowering another.
Optionally, players could enchant themselves up to a certain amount of enchantments. With a similar mechanic to alchemy's "potency"
Stealth
Players could attempt to invade a dungeon causing the least amount of chaos possible for greater rewards.
Enemies would be alarmed by traps or by simple line of sight, but hardly due to hearing combat.
Players that do not stay hidden will end up attracting more enemies at a time, making fights harder. Some enemies may also damage loot when alerted, causing loot they where guarding to yield less rewards.
Hunting
Players could take bounties involving finding and killing a specific monster type.
This kind of activity does not grant any sort of marker or clue, it instead falls on the player's knowledge to find where a monster may be hiding.
The bounty may be for a specific monster instead of a type, in these cases the monster will be more powerful than their regular counterpart, and may often avoid fighting entirely, making players have to plan ahead or setup traps to get a chance at combat. Once
Monsters of this kind may roam around the entire map and have ways to remain hidden.
These monsters will often leave clues on their wake to give players an idea of where to find them.
in combat, these monsters will prefer to stop fleeing.
Artifact trading
As part of the usual loot, players may find seemingly useless scrolls, carvings or relics that someone COULD be looking for.
Players may keep these for later selling if they find anyone looking for them, but are otherwise nearly worthless when sold at a shop.
There is no guarantee that someone is looking for any of these, NPCs may randomly decide they want an artifact of X kind which may or may not exist in the world yet (from a code stand point).
Negotiation quests
Sometimes, a quest may involve getting something from another, random NPC.
The target NPC will usually want something in return, players may negotiate by offering to complete a quest for the target or simply by paying with specific items or gold.
Different targets may or may not accept certain things.
If the NPC is neutral or there is some justification for it, the players may fight them for it.
Players with high charisma or a related skill may attempt "rolls" on the target to reduce the requirements from the target, possibly completing it instantly.
Faction relations
Players may improve or harm their relations with specific factions due to a variety of activities.
Some quests may include a shift in faction relations towards the participating players
Some factions are in conflict with each other, in these cases, increasing/lowering relations with one past a certain point will affect the other. (improving relations with faction A from "disliked" to "neutral" will have no effect, but reaching "friendly" will cause their enemies to loose relations with the player)
High relations will cause the faction to give the player better prices and some other benefits.
Lowering relations enough will cause the player to be barred from entering the faction's "cities". Players may still accept quests from them, which will raise relations.
A side activity would be anything outside of the main combat loop. Things like collectibles, crafting mechanics, etc. I don't know what the consensus is about these, so i propose a few to discuss about.
Alchemy
Enchantments
Stealth
Hunting
Artifact trading
Negotiation quests
Faction relations