Any small gravel is fine, whatever the source. Use what came with the tumbler, but there is no need for the polishing compund unless you want mirror finished coins. Actually, that may be kinda neat, when you think about it....
Partially fill the tumbler with gravel and coin, leaving about 1/3 of the tumbler's interior as free space, so you get good tumbling action.
Then, I recommend a 1/4 cup of houselhold cleaner Formula 409 and water, enough to cover the gravel/coin mixture. I often add a piece of steel scouring pad, too, but it really isn't needed.
Finally, set the whole shebang into a large plastic pan and turn it on.
The large pan is there in case you have an accident and the tumbler comes open for some reason - dont ask me how learned this lesson 
Now, go away for 5-8 hours. You can leave it running overnight if you like... it hardly makes a difference. I've found that 5 hours is about the minimum, though.
When you open the tumbler you'll have nicely cleaned coins.
DO NOT mix clad fractionals (halves, quarters, dimes and nickels) with cents, or everything will turn an unsightly coppery color. Unless, of course, you like your money to look that way.
And it should go without saying that you should never tumble clean silver/collectible grade coins.
Beach coins probably wont come out looking like mint coins, however (heck, most coins don't, regardless of their origin). But it will certainly improve their appearance.
Remember, this wont turn old coins into new ones. It just knocks the crud off of them and "nicens 'em up," as we say in these parts.
