Anything that works the "climbing uphill" muscles will help you prepare for hills. In a gym: stairmaster, step mill, versa-climber, treadmill on incline, or step aerobics class. If outside of a gym: stairs, hills, or even pseudo-hills like a bridge. You can walk, jog, or do intervals. It's hard to prepare for the downhill segments (which can be just as hard with a heavy backpack!), without getting on some kind of actual hill. Squats and lunges (I like walking lunges) are also great leg strengthening moves.
It's important to do some all-around strength training too -- you need a strong core and arm muscles for carrying that back pack and luggage.
Make sure you get good quality, comfortable hiking shoes -- and break them in well before you go! Also, invest in good quality hiking socks and clothing that is not cotton (cotton kills). You want something that is rugged that will wick out moisture and evaporate it. Take layers so you can adjust to changing temperatures and conditions.
It's great that you're going on a trial camping trip, that will be an ideal opportunity to check out your gear so you can make adjustments before the "big" trip later! Sounds like great fun!