Tacticool is never my goal- form follows function and as such I try to avoid hanging espresso makers or cheese graters off a picatinny rail. With that as a disclaimer there are a few items I have discovered that are must have items if you own a gun. Once in awhile I will share those finds- hopefully you find them useful in an ocean of accessories.
The thing I hated most about cleaning guns when I was a kid: the pushrod and the bore- wet a patch or 3 down with solvent, ram it through the barrel, repeat until you get a clean patch- which is like 10 times. Trust me, this takes forever- no matter what age you are.
Enter the BoreSnake– it's simply brilliant: let the cord with the weight drop from breach to muzzle, pull the snake through the barrel once or twice (less than 5 seconds per pull). It has solvents and textures and perfectly fills the barrel to ensure an efficient and respectable clean bore. If you don't have one of these yet get one now…at the LGS (local gun store) or interwebs (MidwayUSA or Brownells are good spots). I suspect you will end up with one for each caliber you own.
One thing that most Glock owners can attest to is that they are more slippery than a CongressCritter if your hands get wet. The Gen4 Glocks appear to have solved this problem but until I'm lucky enough to try one I have the Tuff1 gun grip (similar to the one pictured below).
The Tuff1 grips are ridiculously simple and make a serious difference on any polymer or other basic pistol grip. The grip on my Glock is amazing now- the Tuff1 gives it a hard-gripping rubber with enough cushion that I can compress it just enough to offer a rock-solid handgrip. It actually took some time to get used to the grip when drawing the pistol because my hand wouldn't slide over the back of the grip like it used to- my hand sticks to this thing like its made of glue.
These also make a big difference on the A2-style handgrips you get with basic AR-15s or lower parts kits. The cushion effect of the texture really adds comfort and precision to your grip. Also they are probably the cheapest accessory you will ever find: they run about $17 each. And you can get one with skulls on it! Although that could be construed as borderline tacticool I won't say a word.