One can enjoy many hours in an arcade, even with a very limited amount of money. First you'll need some materials though. Here they are:

Now, cut off about 12 to 18 inches of thread. Tape one end of the thread onto one side of the quarter. Use as little tape as possible, but make sure the thread will not break off easily. It seems to be best to place the thread straight across the centre of the coin, covering the whole length.

Wrap the thread around your index finger a couple times, and lower the coin slowly down the slot. This is the tricky part. You'll need to feel for when it reaches the point where it passes through inside the big money box thing. Once you've found the spot, just gently lift the thread enough to bring the quarter up a little bit.

If you've done well, you should notice a credit showing up on the screen. Repeat this process until you get bored, the machine won't give you any more credits (most stop at 99 I think), or someone starts looking at you weird. And then of course, enjoy your discounted gaming experience. Leave some credits for kids to use up, it'll make them happy.

This doesn't work on the newer arcades, and some are likely easier than others. I haven't tried it in a while, so your results may vary.