Parade Tips

This is what you can do:

bring a whistle and use it as much as you want! Isn't it what you have always wanted to do?
bring a drum and play without worrying about the rhythm
make a banner with your slogan or your message.Let everyone know!
make a costume and wear it. It is very easy. Don't have a costume? Do not worry. It is not mandatory.

Other ideas:

choose your marshal, a leader who will carry a banner with a name of your group, if you are marching as a group of course
sing the slogan you have chosen (eg. Give Peas a Chance)
bring your instruments to help you sing (drums, sticks, maracas, etc). You can make your own - just fill a container with dry seeds - rice/chickpeas/nuts of your choice.
organise a cd player if you wish to play your song you have recorded earlier. Remember about the batteries!
bring your bicycle and make it look good :) either as a fruit/veg or carrying a banner - you can ride it or walk it...
make a fruit/veggie structure like a puppet you can move while marching. You can make it from paper and cardboard and a bit of timber
decorate your hat with some fruit and veggies
search the Internet for inspiration. Look at some costumes. Remember to register to try your luck in the Costume Contest.
if you don't have time to make costumes, your group can wear same (colour) t-shirts...
bring some baloons