Building team chemistry?

I guess it would depend on age but with my 15u team I've done several things outside of the normal happenings (Hotels or dorms during out of town events, swim park, etc....). Doing events where the team can have fun outside of the baseball part is probably the best. Day to day though.....

Practices in the rain have been HUGE in my players bonding. We practice sliding in the mud then play football in the wet outfield.

Every now and then instead of normal practice we will simply play whiffle ball. 

Instead of practice take the team to a movie. 

THE most successful things I've done are those that don't actually include playing the game itself. They work hard enough as it is between travel and school (ball and academics) that sometimes they just need to be a kid. Putting them in a team environment away from the game is the quickest and easiest in my opinion. 

Play baseball golf after practice.  One version you fungo it.  The other version you leave it on the ground.  The bases are the holes--1, 2 and 3.   Hitting the base is the object.  Have the players pick two teams.  Losers run the perimeter of the field (once).  Also can be done like croquet, which eliminates the need to keep a scorecard.  The first team to have all its players hit first, sec., third, and home wins the game.

Mix in team competitions, contests and games as often as possible.  i.e. ...

-  Sometimes, for conditioning, we'll have them play ultimate frisbee.

 - Many of our practices will be live speed game w/coach pitch.  Pitching is progressively complex by inning (from about 50'). Teams sprint on/off - as soon as hitter is ready, pitch is thrown.  We can get a 9-inning game done in an hour and they always want more.

- Rainy day pizza/hit philosophy discussion.  Keep it short and leave some time for just them. 

- Team relay throwing drills.

- Team execution contests like 21 outs.

- Team bunting and hitting contests (using cones).

- Player choice practice time.

Be sure to schedule a few away games that require a couple hours in vans or buses.