Actually, Academy gear will work for backpacking - it's heavy and bulky, and it may wear out sooner, but it will work (I used that kind of gear my first couple of years, replacing it as I got some experience and learned what features I really valued in gear. Of course, I also was a bit limited in when I could backpack and how far I could hike in a day - but I still had fun.
You don't mention a stove or cook kit - if you don't already have something, that might be your first investment My own preference is Snow Peak, though I'm toying with the idea of a Toaks alcohol stove and pot set. Depending on the trips you're taking, you might consider a water filter (in my case, a Vecto 2L bag and 1L Vesica bottle, both from CNOC, and a HydroBlu VersaFlow filter.) If you have those, I'd probably upgrade my tent first, then sleeping bag. (A good tent will give you a better shot at keeping you and your sleeping bag dry in bad weather; a wet expensive sleeping bag is just as worthless as a wet cheap bag.
If you're needing to replace several pieces of gear or need some clothing, you might take a look at REI's house brand of clothing, packs, tents, and sleeping bags - a little on the heavy side (but probably lighter and better quality than you've got now), and usually well-made and more affordable.