I used to run a Schwinn rack on my old wally world deathcycle (there might be a pic under my account somewhere on here), then I tried it on my GT, then took it off after a few minutes. if they make them for different seatpost sizes, make sure you get the one for the seatpost that your bike uses! it may sound like common sense, but if you’ve got a 30.6 or a 31.6 seatpost you might end up high and dry when it comes to luggage racks that will fit your bike. of course, rather than a seatpost-mounted rack, I’d just spring for a particularly large under-seat bag. Topeak makes a few, one of them being big enough for a 6" turkey delux w/ cheese from subway once you expand it, and for a drink, your camelbak should work fine, and give you a little more storeage for stuff like tools or the occasional candy bar