Pocket protector
Another feature your tennis bag could never have too much of is pockets. This prevents rummaging through your bag searching for those small items like grip tape. Pockets also add a bit more security. Chances are (when playing) you'll probably keep your keys and wallet in the tennis bag. You also probably won't be paying too much attention to your bag during the match. For this reason a pocket inside your bag comes in handy to hide your valuables from any unwanted wandering hands. Nike & Jet tennis bags that are designed with a plethora of pockets."
Easiest To Break Strings
Longer tennis strings on a string bed move more hence break easier (see larger frames from above).
Another Ball in the Wall
If you don't have a partner, ANY wall will groove your ground strokes. Try this free tennis lesson on your own. Play up close to the wall to hit the ball in the center string as much as possible. Then, move back and let the ball bounce twice against the wall, hitting the ball softly! This will give you the rhythm and timing essential for ground strokes!
High Pressure
If you play 3,500 feet or more above sea level, get " High Altitude" tennis balls. They are not as highly pressurized as regular tennis balls, which, in the lighter air of higher elevations, can be too active.
Numbers on the balls
Numbers on the tennis balls are right under the logo. This is so that when you have, say, 8 adjacent courts and some are using the same brand or type of ball, then there won't be a mix-up of someone's ball sprays onto the other court. Unless, of course, they're both using the same number tennis balls. For instance, if you are using Penn 3s, the court on your left has Penn 1s, and the court to your right has Wilson 3s, you can tell at a glance which court to throw the extra ball to and in turn they can get your lost ball to you easier.