Ideas for a Christmas Day Scavenger Hunt in the woods?

[TooMuchTV]

I had the idea of trying to drag my niece and nephew (9 and 7) away from their computer games on Christmas day (and wear them out a bit ) by taking them out for a walk in the woods. I thought that making it into a scavenger hunt with prizes might make it more appealing...

Idea so far:
the largest pine cone
the longest feather
the largest collection of different leaves (with double points for those correctly identified)
the largest number of items of litter (there is a bin as we leave the woods to dispose of them but I have a slight concern about what they might pick up)
longest/widest leaf of any type

I don't have much imagination with these things - does anyone have other suggestions for things we might look out for?

we were out in the woods today, and spent ages trying to find some holly that had a berries left on, we just found 2 bits.

how many beetles under logs etc

we sometimes played the alphabet game, we had a central point and they had to find something beginning with each letter, which is hard, but can turn out very funny, as they make up all sorts of things, and have hard letters in the middle of found things, ie K hard, but bought me bark.

Something shiny, something long, something round, something furry, something brown etc

Ooh - hadn't thought of asking for things described by adjectives like something round, furry etc - no shortage of brown things in the woods at the moment!