The best bridges at a minium weight are toothpick bridges that are truss bridge designed.
The best way to design your bridge is to first look at the different types of bridges built by engineers today.
[url]
http://www.brantacan.co.uk/truss.htm[/url] for some excellent theory and examples.
Don't use the wimpy toothpicks that you typically find in the grocery store. Coloured cocktail toothpicks are very strong and make for a good structure. These are usually found in the picnic or party section of your grocery store.
Good glue is a necessity for strong toothpick structures. Use a fast-drying epoxy type glue for maximum strength and workability. Wood glues are also good, but take a long time to set. If you decide to use epoxy, be very careful with it. don't use SuperGlues,they're expensive& do not have good long-term strength and will not give you the best results on porous, wooden sticks.
If you do choose to use the wooden ones,You can also soak the toothpicks to make them bendy..if needed..