Velcro.  One of man's most amazing inventions only second to Duct Tape.  For those of us who have multiple camo patterns and need to swap team patches and name tapes, it's a convenient way to do so without a lot of hassle.  Here's a suggestion on a great place to purchase your Velcro for a decent price.

Those of us at SOG usually carry around a map of our 130+ acre field even though we play there every weekend.  It's a great way to orient walk-ons and cadets when setting up a strategy for an objective or op.

As useful as they are though, it's hard to keep one that doesn't eventually fall apart, even if they are laminated.  I found this article on Instructables that show how to create a lightweight, waterproof map.  I haven't tried it yet, but thought I'd share with the rest of the airsoft community.