Sorry you missed out before!

Jim's usual policy is to sign three books per person per trip through the line.  At most signings, if folks have more than three books, they can go back through the line for another three, and lather, rinse, repeat.  However, as there are so many folks at Dragon*Con that many can't get through the line even once, there can be no second helpings. 

Of course, when you see Jim, you're welcome to ask if he'd be willing to sign your remaining books afterward.  This isn't something I'd encourage, as Jim has to stop signing books sometime, and cons usually keep guests pretty busy.  He may have another commitment afterward that prevents him from lingering, and if he does have time to linger, he may prefer to prioritize fans who haven't gotten anything signed yet.  There's no guarantee if he'll say yes.  You'll have to decide whether the effort of carrying all those books a mile and back is worth the risk.

As for "gifts," Jim doesn't drink alcohol, but he digs Mexican Coke--the kind with real sugar, rather than high fructose corn syrup.  Coke keeps him ambulatory at cons! 

Also, side note: fans giving gifts should be aware that Jim likes to travel light, usually with one carry-on bag.  If the gift isn't something he can easily travel with, you might want to offer to ship it to him, so he doesn't have to worry about getting your awesomeness home.