Pineapple
You can use this cheat option to blow up any balloons that come near the area where you drop it. A pineapple will explode within three seconds of hitting the ground, so make sure you're ready for it to go off when you queue one up.
Boomerang
Boomerangs will leap out from the towers where you place them, kill multiple balloons at once and then promptly retreat. You even can use your unlimited gold to purchase the expensive "glaive thrower" upgrade for your boomerangs.
Monkey Beacon
A monkey beacon increases the range and attack power of all nearby weapons. This makes it one of the most powerful items in the game, and since it is now totally free, you might as well place as many as you want along the course. You can also use your unlimited money stockpile purchase a speed upgrade for your Monkey Beacons.
Road Spikes
Road spikes sit on the path wherever you place them waiting to pop any troublesome balloons that stumble along. Normally spikes wear out after doing their duty with 10 balloons, but with unlimited money, you can place new spikes as soon as the old ones disappear.