If you haven't done them before, then go with body weight or just the bar.

When I was in college, I used to pretty light weights and a lot of reps - 85 to 100 pounds max. A couple of years ago I read the New Rules of Lifting, and did one of the programs from that book before running one of my marathons (I finished the program about 2 weeks before the race.)

Instead of going lower weight and higher rep as I got closer to the race, the program had me increasing the weight and lowering the reps. I wound up squatting about 240 pounds and deadlifting about 200 pounds for a minimum of 8 reps per set. At the time I weighed about 135 pounds, maybe 140 pounds. It was easy to set PRs when I hadn't really lifted heavy before.