Don't always assume that tours are going to be bad for your budget. Especially if you manage to add them on, or get them on sale.
I've traveled on both bus tours and cruises which have been cheaper per day than they could have been if I was paying for transport, food and accommodation separately. Not to mention, on the bus trip I saw places I might not otherwise have been able to see.
If you are on a cruise, or you've got a hotel with a buffet breakfast included, don't be afraid to stock up for lunch as well as breakfast.
They might frown on you for doing it, but if you don't make it too obvious you can make some excellent sandwiches out of a buffet breakfast, and then just have a light dinner on the town.
If you have to, sneak those apples out in your shirt!