You will probably get some pretty good antenna suggestions here, but I want to caution you in case this might be your first attempt at QRP. Since 40 meters is the band you will be using, the antenna you select needs to be as good as you can possibly make it. So, if there is any way you could go with a dipole, and maybe even just one of those collapsible poles for a support, you may find that works a lot better. I've operated QRP on 40 a bunch, and often with just something much simpler, like an MP-1 or similar, but 40 is a tough band for using small portable antenna systems like that. You really need to pay attention to putting out a good ground radial system. If you do, you can have some very good results with smaller systems like that. An End Fed Half Wave, or even one of the Mag Loops might be a good option too, but both have some disadvantages. Even a random wire and a counterpoise can work well, but you probably would need some kind of tuner. There are some very good small tuners--like a Z match--that will do a good job and not take up much space in your pack.
Check out what some of the SOTA folks are using for antennas. They usually have it down to a science as far as keeping things as simple as possible while still being effective.
Good luck and hope you have lots of fun with that rig. QRP is a hoot once you get into it.