Each boat varies in terms of the daily checks required and you should always refer to the handbook given to you when you are handed the keys to your holiday boat.

Here are some general checks that are often required with motor boats

Water Its often advised to fill up your water daily. If you keep it topped up you should not run short. Holiday Boats have limited storage for water and a couple of showers can diminsh supplies.
The dashboard Monitor the guages and warning lights on the dashboard at all times. Make sure you have a good battery chargem the oil pressure is OK and that the engine is not overheating. Many boats have a warning buzzer or light if the engine is overheating. If this goes off - stop the boat immediately and moor up and ring the boat yard for advice.
Bilge Pumps Most boats its ok to leave electric bilge pumps on all the time. If not, or you have a manual one make sure you pump the water oout each day. The last thing you need is water coming up over the engine. The boat will eventually sink if the bilges are not emptied of water although it is likely to take a long time
Fuel Most boats come with enough fuel for a weeks cruising. Often a dip stick will be provided if needed to see how much fuel is left
Electrics Many modern hire boats include 240v electric, TVs and music. Take care not to run these too long as they will drain the batteries. Usually the 240v is provided through a power inverter. This should be switched off after use.