First of all I'd try to think of every active way I know of to teach everything I teach. I am not sure how your day is set up or how you approach each content area, but here are some things I would do.
Open School Ideas
Check out Rebecca's "Story Picks" post on the Third Grade Board under "creative ways to teach writing" -- about 1/4 of the way down. It is a very fun, creative way to do a writing activity. Before actually doing Rebecca's activity, I read a picture book and had students identify the elements -- character, place, things -- that I wanted them to include in their writing. Then I followed Rebecca's plan but first had students write a group story to share with the class. (Parents could easily be part of these groups.) Then I had individuals draw out the character, place, things that they would include in their own story. This activity could be completed over a 2 or 3 days depending on the amount of time you give groups to write and share before allowing individuals to write on their own. You could even have parent-led editing groups where students read their stories and get ideas for making them better. Then on still another day, final drafts could be illustrated, shared aloud, and placed in a class book.
Again, I'd choose some activities that adults could join in with the kids. Maybe everyone create a wordsearch for parents to solve, or one day students write spelling words on index cards and the next day 2 students combine sets to play concentration -- matching words -- with parents joining in.
Math games in which parents could be active participants would be my choice. I do simple games that require little preparation sometimes. For example: Use regular playing cards (with face cards removed) to play multiplication war by having each player draw 2 cards, finding the product, greatest product wins all 4 cards. We also just use dice to get the numbers we use to practice adding, subtracting, and multiplying.
We do Reader's Workshop and students read and write on a regular rotation schedule. I would just continue my regular plan and let parents join in with readers or form discussion groups where students can simply share what they've been reading. Kids love having an adult ear to bend.
Could you find a play that fits in with your content in such short notice? Maybe you could do a geography scavenger hunt of sorts using maps, globes, and atlases.
Could you do some kind of exploration where students carry out the scientific method. Maybe predict ways to increase heartrate (run in place, etc.) and have them set up ways to test their hypotheses -- gather, organize, graph, analyze data? This kind of activity could be integrated in with math as well.
It's difficult to pull together a whole week, but whatever you do, just relax, be yourself, and have some fun. Good luck!