Pickpocketing has a carry limit +100 perk iirc, can also enchant items with carry limit+ enchant (I found a necklace on some guy with +25 carry limit). Other than that I think leveling up slowly increases it, maybe every 5 levels or so? Mine keeps going up by itself every so often. Also had an awesome glitch earlier, half the terrain outside the Companions building didn't load, I could just walk around underneath the Skyforge. Apparently there's a hidden chest inside the terrain that the NPC uses to store his items and gold for the shop, and it let me loot it (didn't count as a crime), got a ton of free shit and over 1k gold from it, lol.
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