You will need:

3 plastic foam meat trays
2 plastic drinking straws
1 plastic bag for sail
1 pattern for body.

How to:

1) Using the pattern that you pre-made, Beavers cut three hulls and glue all three together.
2) Cut a sail from a brightly coloured bag, and glue it to the straws.
3) Poke a small hole in the first two layers of the hull, and insert the mast. Glue to hold it in place.

Source: York Summit District Crafts for Beavers