My pack is also about 2400 cubic inches (~40L). There's additional capacity in the extension collar, but I've never needed to use it, even for 9-10 day trips. My understanding is that the standard measure of pack capacity includes the extension collar but not outside pockets. Of course many manufacturers don't follow the standards.
The side pockets of my pack are full-length (of the main pack) and have an elasticized top, so stuff doesn't fall out. I do use those side pockets; my tent and fishing rod are in one side pocket and my water bottle and snacks in the other. I like having my tent where I don't have to open up my pack to get to it if it's pouring rain when I make camp, and so I don't have to put a soggy tent inside my pack with the dry stuff. (I may change this in the future.) Should I ever get a pack with short side pockets, I'd want it to have several good side compression straps to hold stuff on, and I might use a piece of cord for additional security. I use the back mesh pocket only for a few small light items (it's a great place to dry wet socks). Admittedly, I am normally on trail and rarely if ever try bashing through brush. Slide alder and devil's club (what we have out here on the west side of the Cascades) are just not my thing! If I go off-trail, it's in alpine country.
If your tent poles are longer than your pack, I strongly suspect that your tent may not really be suitable for backpacking. Unfortunately not all tent designers are backpackers! The poles for my tents (all Tarptent designs) all fold to 20 inches long, and the tent stuff sack is 22 inches long. I believe this is a fairly standard length for a backpacking tent. I just checked the "packed size" for three manufacturers, MSR, Big Agnes and Sierra Designs. Their packed lengths range from 18" to 22", and that should include the poles. Check the manufacturer's website for your tent to find the "packed size"--the longest dimension should be the length of the folded poles. If you can't or don't want to return the tent, I'd follow oldranger's suggestion. Be sure the poles are tied on very securely, and check them every hour during the day. If possible, utilize one of the your pack's side pockets which will prevent vertical slippage.
Edited by OregonMouse (12/23/11 02:15 PM)
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey