Breaking the rules + appropriate sanctions

[CeliaFate]

I don't allow the dc to eat snacks in the lounge, I ask them to eat at the table. This is after ds ruined a very expensive leather sofa when he tipped hot chocolate all over it, crisps and biscuits trodden into the rug etc.
I go into the lounge today - dd is on the sofa with a bowl of effing cereal, the bottle is put on the wooden table (no coaster, natch) and she's tipped dry cereal over the rug that I've cleaned today.
WWYD?

First my DD would be clearing up the spilled cereal then I would be putting the cereal in a place she couldn't find it.
My DD was sitting wiping her hands on one of our sofas at the weekend. I was furious and I doubt whether she'll do it again anytime soon.
It is so annoying, I know my DD understands when I say no food out of the kitchen, but it seems to get scrambled in her brain as soon as I am not around.
Do you set an example to her? If she sees you slurping up shreddies on the sofa it must make a little voice in her head tell her that if mum does it, it must be OK.

I never eat in the lounge, she likes to so she can watch tv at the same time! She cleaned it up and was most put out when I turned the tv off, "I was watching that!" she cried. Tough titty! (I thought, but didn't say)