Definetelly :D This post is just a non-thorough idea :) Never been tested by the poster :P
Everyone here is right - stuff goes back to your inventory, when you unsummon. You would have to bring him around with you.
Here's a thourough yet dangerous idea: Bring your pet to the place, where you shall gather xp, kill the pet and for 20 minutes you have portable storage :D When you need to exchange stuff - ress the pet, exchange and kill again :D
Just don't forget to reresurrect it every 19minutes. After 20 minutes it will disappear and bring your stuff with it :P