I'll take a shot and say you probably don't need an extra battery...until you start taking enough pictures to run down the battery to very low levels between charges. Lenspen? Maybe. I'd go with a microfiber lens cloth before a Lenspen. I have both, and so far, since I got them in December, I've only cleaned my glasses with them. More memory cards? Only if you find what you have isn't large enough to handle a day's shooting. I started with an 8 gig card on my 30D, and got a 'spare' 16 gig, which I never used before I moved up to a 60D and different memory cards.
I think I'd start with something to carry your gear around in. When I'm going somewhere, I have 3, progressively larger bags to carry my stuff with. I usually use the smallest, that's good enough for one body and a couple of lenses. The two smaller, gym-sachel size bags are from Walmart. Doesn't have to be anything fancy.
As mentioned above, go out and shoot. See what kind of photography you 'fall in to'. Maybe it's busy downtown city shots, or architecture, or people-shots. I was taking pictures of this, that, and anything before I started taking pictures of my hobby interests, trains, about 45 years ago. That REALLY got me into photography, big time. But as my interests changed and I grew older, my subjects changed. Bottom line, you won't know WHAT you where to focus your interests as well as your camera until you try this, that, or whatever. Starting with your hobby, like I did, could be a good start. You might find you want to do small, close-up work (macro photography), or taking pictures of ships on the Great Lakes, in which case you'll need some good telephoto lenses. (I see you're from Michigan).
In all liklihood, you'll need a decent tripod to hold the camera completely steady, to get the sharpest pictures. The really good ones cost more than you paid for your 40D and lens. Before shelling out that kind of money, check out Craigslist and
Ebay. I lucked out and bought what was comparatively cheap 35 years ago, but by todays standards, is rock solid. No fancy ball head, but I can point the camera any way I want with it and lock it in. Don't look for cheapest, here. Use Google to check reviews on whatever you're thinking of buying, as well as online photography equipment 'dealers'.
If you're doing any indoor work, you'll also want a 'real' flash unit. The popup on the 40D, and all popups in general, are good for about 10 feet of illumination. Beyond that, they're useless. Again, you won't likely need the top of the line Canon 600EX-RT flash, but a decent, mid-range flash, such as a 430EX, would be a good start...
So, save up some $$ for future acquisitions, perhaps meet up with other local photographers and 'pick their brains'. There's a tendancy to buy everything you see, like a kid in a candy store. That gets real expensive real fast. There's no rush to see how fast you can get more 'stuff'. But most of all, HAVE FUN!
PS...almost forgot to mention...you may need to upgrade your computer to handle photo storage needs (and backup in case of a crash/fire/theft!) as well as some photo editing software such as Adobe Photoshop Elements or Lightroom.