The problem with coming in cold to bodyweight exercises like pushups and chins is that it may not be at all OK to do 5 today. The great advantage of using weights or bands is that one can use lighter ones and higher reps, thus conditioning the connective tissue without risk of injury. Even milk jugs with water or juice cans work.

The best weight training resource I know of is exrx.net:
http://www.exrx.net/
http://www.exrx.net/Lists/Directory.html