Its just plain silly to think that a dwarf would make 5 separate trips down a 50+ Z levels to snag up 5 gems lying next to each other (mined from the same cluster). The things are light as a feather! While holding 5+ small items at once is tricky, bags and backpacks already exist in the game! They can even hold things! So instead of trudging up/down that mining shaft 5 times to pick up 5 gems lying right next to each other, Urist McLazybutt grabs ONE bag and makes ONE trip to pick up those five ADJACENT gems! That wasted time is time he could have spent getting drunk in your legendary dining room! Or having FUN with goblins! This would also be huge for plant gathering. Why travel 50+ squares one way to drop off a single sunberry only to trudge right back and harvest from the bush directly next to it? Urist McHippy would be bettery off equipping his backpack and harvesting all bushes in a zone/filling up his backpack before dropping them off. Those good-fer-nothing fisher dwarves could even -gasp- carry their entire haul back the fishery instead of leaving them to rot by the river! Legendary Cheesmakers could spend one afternoon combing a battlefield for reclaimable bolts, isntead of spending the entire season bringing them back one at a time. The possibilities are endless!
Its not like dwarves can't grasp the concept of using containers to carry things- they already haul entire bins of useless fodder.. er "finely crafted mudstone trinkets" to the trading depot, and hauling dwarves already carry around containers... but the poor things just have it all backwards. The dwarves will drag an entire barrel through the swamp and up that steep hill just to pick up one whip vine before repeating that whole process again... after returning hte barrel and picking the bush next to the first for some prickle berries. They don't even store multiple items next to each other after lugging hte barrel/bin all the way to the middle of nowhere!
The backpacks could even be considered required equipment for certain labors (or at least preferred if available/configurable). Item hauling, food hauling, fishing, etc could all require a backpack to pick up multiple small things. Bags could fill this role as well. Each time the dwarf picks up an item, he could check near him for another (unclaimed item) and pick that up too. Once hes filled his backpack/nothing left to pick up, he'll return to base and drop off the contents in the appropriate stockpile. Weight already affects carrying speed based on strength, so dwarves would only pick up enough small objects that they could comfortably carry, or only so much that would slow them down to half speed. Containers already have size limits as well, as you can make roasts too large to fit in barrels/only so many trinkets/bars go into a single bin, etc. The only problem I foresee, is when a dwarf picks up more items than will fit into a stockpile- especially if many dwarves try to haul for the same stockpile. In that case, whatever can fit will be dropped into the stockpile. The remainder can stay in the bag and dropped on the nearest open tile. This would ideally generate an announcement proclaiming that the stockpile was full/items dumped.