There are some basic cleaning supplies you should always have on hand.  Messes happen.  If you can't clean them up immediately, they only get harder to clean. 

Here are the basic things you should never run out of:

• Laundry detergent (treating a stain immediately can save a piece of clothing)
• Broom and dustpan
• Vacuum (small or large) and extra bags
• Lint free cloths for dusting, cleaning windows, etc.
• Washable sponges in several sizes
• Mop
• A good all-purpose cleaner that can be used for bathroom fixtures, counters, floors
• White vinegar (an incredibly useful cleaning agent when diluted)

You don't need a ton of stuff with a unique cleaner for every surface (unless you have granite countertops or a ceramic cooktop or a fiberglass tub that requires a special cleaning agent).  Most things can be cleaned up with an all-purpose cleaner as long as you get to it right away.  The key is having something on hand and using it quickly when something happens and regularly the rest of the time!