Does anybody know a good bodyweight exercise for traps and neck? I have tried the inverted shoulder press but would appreciate other suggestions.
I like to grab a pull up bar and drop one hand hang at full extension then switch to the other hand. As you switch you trap will be engaged to lift you up to switch hands. The longer you can sustain the state between hanging on one hand and grasping it with your other the more completely you will utilize the trap.
The best bodyweight substitution for a weighted shrug is just a shrug from the inverted hang (aka inverted shrug):
This can be done on rings, straight bar, or even parallel bars:
Shrug Dips or Dip shrugs, whatever Kelso calls them are very effective. you get in the position of doing Dips and instead of going down push yourself up, hold this position and then lower your self down. the actual movement should be no more than 6 inches. your elbows dont bend during the whole repition. Search the internet for Kelso's dip shrug and you will get more detail on how to do it.
Bridging drills from wrestling, both forward and backward, are awesome for neck strength.
Handstand "shrugs" were recommended to me as a drill for developing the traps as well as all the muscles that assist with scapular retraction. You get in a handstand (against a wall is fine) and simply relax the shoulders forward and "down" towards your hips, then squeeze them backwards and "up" towards your head, towards a proper full handstand position. The shrug dips described in Geek's answer sound similar.