Alas for clear-cut answers, I'm a writer, so more than one word comes to mind in many cases.
1. A body of water, smaller than a river, contained within relatively narrow banks.
Stream or creek
2. The thing you push around the grocery store.
3. A metal container to carry a meal in.
4. The thing that you cook bacon and eggs in.
One can do that in several things; I suspect Frying Pan is the expected answer.
5. The piece of furniture that seats three people.
Sofa or couch
6. The device on the outside of the house that carries rain off the roof.
gutters and rainspout
7. The covered area outside a house where people sit in the evening.
Covered area? Porch. If it's UNcovered it's a deck.
8. Carbonated, sweetened, non-alcoholic beverages.
Soda or soft drink
9. A flat, round breakfast food served with syrup.
Pancake or flapjack
10. A long sandwich designed to be a whole meal in itself.
11. The piece of clothing worn by men at the beach.
Wetsuit? :) Swimming trunks or bathing trunks
12. Shoes worn for sports.
running shoes or sometimes sneakers
13. Putting a room in order.
Depends on how much putting in order you need; tidying up implies very little work, cleaning implies a lot more.
14. A flying insect that glows in the dark.
15. The little insect that curls up into a ball.
Sowbug or pillbug
16. The children's playground equipment where one kid sits on one side and goes up while the other sits on the other side and goes down.
17. How do you eat your pizza?
I generally cut it up and eat it -- knife and fork. If the pizza's of JUST the right consistency and temperature I may pick it up and eat it as a slice.
18. When private citizens put up signs and sell their used stuff.
19. The evening meal.
Supper or dinner
20. The thing under a house where the furnace and perhaps a rec room are.
Basement or cellar
21. The thing that you can get water out of to drink in public places.
I know these have alternate answers, so I'll be interested in seeing how common the different ones are.