I am baby sitting two kids this summer and need some ideas?

I am baby sitting a 7 year old girl and a 4 year old boy for the summer. I watch them during the day on Mondays, Tuesdays, and Wednesdays and in the evenings on Thursdays and Sundays. I am trying to find some things to do with them that cost little money. I can drive and take them places but they are naughty little kids. They don't listen very well and often throw tantrums and think they rule the house. So i don't like rewarding them by taking them to the park after they are bad and stuff. I want some things to do in the house. They are messy too so I don't want art projects and things like that. They have been banned from kool-aid even, because they spilled it everywhere. I need soem ideas on discipline and activities. It would be greatly appreciated.