Ideas for a scavenger hunt in the park?

[chicaguapa]

Am going to take DC (7&4) to the park tomorrow to do a scavenger hunt as the weather looks like it's going to be nice. Any ideas what they could look for? So far I've got (not very inspiring and a bit repetitive ):

Twig with two bends in it
Moss
Green leaf
Red leaf
Brown leaf
Rock
Blades of grass
Yellow flower
Red flower
White flower
Pink flower
Feather

Cool idea - My kids would love this too
I think its going to rain here tommorrow

I wouldnt fancy doing this at our park though - too many unsavoury things too find!

I have no suggestions to add though

you could have a few vague clues like...erm...

something smaller than your pinky nail
something that begins with your own initial
something that has something else inside (snail, unopened flower?)

rubbings? bark, paving, rock, etc.
photos? can you take a digital camera and have things to spot but not collect like a bird, a nest, etc?

Great ideas thanks. I'd thought about the camera but decided they'd fight over who took the photos.