There's a lot of work that goes into an instrumented payload. There's also more choices than ever in the kinds of small, low-power devices one can buy with not a lot of money. I figured I'd start a discussion thread here to get ideas and advice on how to make a sturdy and effective boosted dart.
Measuring altitude is very important. Airspeed would be another possibility. Batteries is another topic, but I think most hobby rocketry uses Lithium polymer cells. The one differences between the RRS and other hobby rocketry groups is the size of the rockets. Ours tend to be slim metal tubes with far less room that the larger plastic or composite tubes.