How many ways, via feats, races, classes, etc are there to increase the carrying capacity of a PC?
As a starter, this answer by HeyICanChan lists some items and spells:
- The waist slot item belt of the wide earth (Magic Item Compendium 204).
- The superior item framed pack (Arms and Equipment Guide 35, 36) - this is 3.0 material.
- The illithid graft hauling back (FF 212)
- The 2nd-level Clr spell lighten load [trans] (Dragon #317 78)
- The feat Natural Heavyweight (Planar Handbook 40)
- The feat Improved Encumbrance (Dragon #292 114)
The answer provides other ways to mitigate the effects of the load, such as using a Tenser's Floating Disc spell or using spells or items that let you be in light load even if you really should be in medium load.
These ways are not repeated here because they don't direclty answer your question, but I suggest you take a look at them all the same.
There are some spells, items or other conditions that were not relevant to that question, but are here.
- Increase your Strenght
- Quadrupeds gets a multiplier, and beasts with even more legs have better multipliers. Polymorph effects, some archetypes and some grafts can give you more legs.