The OEM Kymco belts are very, very good.
3 years ago, I purchased a 2006 XC250 which had 3600 miles on it. The owner had garaged it for almost 9 years, so as part fo the initial workup after towing it home, I replaced the belt with an OEM belt, even though the original one looked fine (rubber parts and aging, after all).
The bike now has almost 17,000 miles on it. I check the belt each time I change the oil (1,200 miles), and it still looks fine and I haven't replaced it since. Keep in mind I weigh 260 lbs. and have a 25 mile commute each way to work - part of it is an uphill climb, and 18 of those miles is typically highway (speeds up to 70mph), both of these place stress on the belt.
My advice would also be to check the belt, and if it looks good, don't bother with packing a spare. I'd be far more concerned with the possibility of a flat caused by hitting a nail.
Also, if you're consistently replacing damaged belts under 10,000 miles, you either didn't use an OEM belt, or have drivetrain problems (most likely damage to the surfaces the belt rides on, but possibly alignment issues).