treasure map 15542 - Many of the smaller treasure maps are not worth the trouble for people to get, but they also do not want to throw them away.
violet potion 9595 - Potions and healing items are always hoarded in every game.
golden diamond ring 8663 - If I remember correctly, golden diamond rings were used to scale from level 90 to 100 in goldsmithing.
wicker basket 7659 - A way to organize a small order of goods.
red potion 5333 - Red potions are useful for training. Guilds will store them up for new members.
leather bag 3882 - The common means of storing items.
horn 2753 - I honestly have no idea. Cows drop them sometimes?
rope 1711 - Ropes are used in very specific situations, and may be dropped from some things if I remember. However, it is rarely worth it to go and sell the rope, so it is stored.
king's crown 1552 - One of the more profitable items goldsmithing, usually made and stored until a proper time to sell.
silver obsidian amulet 1508 - A use for both obsidian and silver, which at times can be over flowing.
sickle 1333 - Not sure why there are so many, one of my characters has three.
charm of the icebird 1274 - A popular status symbol.
hammer 1208 - An average of 7 hammers per person. With different individuals expecting to build, or to build in the future, hammers are often stockpiled.
pick-axe 1196 - Mining is a common activity for when there are few people around, or when a person wants to mindlessly do something. And if a person ever decides to dig a map, it might be needed.
golden topaz amulet 1171 - Valuable goldsmithing item.
bottle of beer 1138 - People buy a fair bit of beer for rp purposes, or make it.
elven composite longbow 1027 -An item previously used for leveling in carpentry.
broadsword 948 - ^ except for blacksmithing.
shovel 929 - People collect sand/clay, but a fair portion will keep atleast one shovel in a depot, if not one in every town, for map digging reasons.
peel 901 - People want to bake the bread.
And here are the stackables:
red elder 797611 - red elders are one of the easiest to find herbs, so they are gathered frequently to scale up herblore.
stone 607403 - Nearly useless item, that is gathered in every mine. It just collects.
arrow 489120 - Arrows get burned through so quickly, it is important to have a ton of them.
copper coins 348248 - This is actually just 34 gold spread across a large number of characters. Just loose change, basically.
silver coins 259814 - This is 1,593 per person. People are willing to trade in some silver, so it's not uncommon to have atleast a couple hundred silver ready for trade usages.
gold nuggets 230557 - Gold nuggets accumulate when looking for merinium.
honeycomb 210401 - I am not for sure on this one. It's used for cooking, as well as candle making.
blackberry 188973 - Used in food, and maybe potions? (Not sure). Fairly easy to get as well.
bough 180807 - These are gathered from a ton of different kinds of trees, and just accumulate. Not nearly as bad as stone.
naldor wood 175488 - Naldor wood is gathered in the process of going for heartwood. It is a less popular resource than merinium, and only shows up in a couple specific instances, as opposed to stone which shows up in every mine.
coal 156940 - All ingots require coal. There is no escaping a need for coal as a smith.
anger berry 156271 - Not sure.
apple 141698 - Apples were previously collected during the 'do little while mc drops' phase. It gave players something to do, while their mc lowered. Having a solid back up food supply isn't a bad idea either.
flour 140014 - Tons of cooking recipes require flour, in the same way that ingots require coal.
cherries 126450 - Same as apples, but less cherry trees exist.
strawberry 123379 - Strawberry cakes are a staple of many diets.
iron ingot 123340 - Iron is used in blacksmithing and armor making, in huge amounts. It's nothing to use 30 pieces of iron in pursuit of a perfect crafted item.
berries 121314 - Not sure, but probably cooking related.
stone block 109657 - Refining stone blocks were a good way to sit at the depot and do something, while not having to do much at all.
copper ingot 109517 - Copper is used a little in all forms of metal working, and is useful to have a few on hand when needed.
As for /why/ characters do it,
Fictionally, it makes a ton of sense. A large bulk of our characters went from close to nothing, or had plenty and it was stripped of them, to learning to survive. Most characters in game are hoarders. Honestly, I find the beginning of the game exceedingly difficult for different character types for different reasons. That leads to a feeling of scarcity, which in turn feeds the need to collect /everything/.
More so, what else is there to do in illarion when there aren't people around? Sorry, but emoting by myself isn't something that is that interesting to me. At least if I am in game, and no one is around, I can collect items while I am tabbed out doing something else.
I could, of course, go hunting or fight some monsters, but that turns me away from people still. Further, if I am not in an ultra-safe position, then fighting isn't really worth it. I might get a little bit of coin, and a bunch of broken junk that no one wants, to sell to an npc for a smattering of copper.
So I collect things. Usually with a long standing goal, or one that I made up. "Better get 1000 apples incase we get besieged by skeletons again!" I wish I was kidding, but that is how my character views the world. At literally any given moment, any terrible thing could happen, so we have to be prepared for darn near anything.
But also, sometimes I am bored, or work was annoying, or whatever. So I really just want to wander the woods and milk some cows, or collect some berries.