We stocked up with cheap drinks from the super market and insisted the kids went into apartment if they wanted a drink as believe me you can end up spending a fortune on Fanta and water.Ice cream also cheaper at super market.
Also large packets of crisps fill them up which are quite cheap, just try not to buy to much at hotel bar as it mounts up with out you noticing.
Pay for things as you get them as they usually like you to pay at the end of the week or day that way you will know were you are up to.
The kids kicked up a fuss as they cant be bothered but they soon got used to it.
Make sure they have a breakfast before they hit the pool, even if its only toast, plate of chips and a butty is suficient for lunch snack.
Shop around for evening meal for best deal, you tend to get large portions which the kids waste so share one between two, nobody cares as long as you are spending something, have a great holiday, let us knoe how you get on.