In a relationship of any significant length, the lines of object ownership tend to get a little blurred. Anything that you leave at his place, he leaves at your place, or you buy together may be up for grabs in a break-up.
Going back to the drawer I suggested in I don’t remember putting that there, put whatever he leaves at your house in the drawer so that your place isn’t messy and so that you know exactly what is and what isn’t his at your place. Should a break-up occur, you can simply empty the contents into a box and hand it back to him (if you didn’t plan a ritual burning of his stuff – which I don’t recommend- it’s bad for the environment you know). It also ensures that you won’t be finding odd souvenirs of your relationship long after it is toast.
I can not stress enough that you shouldn’t leave anything at his place that you can’t afford to lose. We tend to be terrible about absentmindedly leaving stuff at his place. Remember, his place is not your place so if you value your mom’s earrings, make sure they go into your purse, not onto his nightstand. In the event of a breakup, don’t expect him to turn his place upside down looking for everything you say you left there. After a cursory glance around the room, he’ll simply tell you that it’s not there. We get involved in Prince Charming but we break up with Rumpelstiltskin.
The tricky part is when you buy stuff together or are given joint presents. As unromantic as it sounds, keep receipts (not just for insurance purposes). I prefer a rip-the-bandaid-off-quickly approach and leave him everything (if this gets too expensive, you might be being too generous when offering to buy stuff to keep at his place). You’ll gain nothing by making margaritas with “our” blender. However, if you truly love something that you’ve purchased or been given together, consider paying him out his half so that you can keep it. Or barter with him, he can keep the microwave as long as you get the espresso machine. It is not particularly helpful to call dibs on an item when you purchase it as dibs is not considered a verbal contract in a court of law.
As much as possible, keep things separate until you have a legally binding contract to share expenses. Try not to get too emotionally attached to objects, they won’t keep you warm at night (unless it’s a space heater or electric blanket).