Believe it or not, I made a one/two person pontoon boat, out of 5 gal. buckets. To make the same boat I did, you will need the following,

12 Plastic 5 gal. buckets, with lids
6 pieces of plywood, 1/2 thick, about 6 inches square
18 screws 2&1/2X1/4 with two washers, and 18 nuts each
3 2X4's 4 ft. long
6 nylon tie down straps, 8 ft. long
2 2X2's 6 ft. long
1 sheet of plywood 4X6, or two pieces of plywood making up the same length.
LOTS of screws, 1 inch to 1 and 1/2 inch work best for the most part, but you will need a few (12) 3" screws for the 2X2's on the sides.

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First, put two lids together, top to top, by putting a piece of plywood between them, and drilling three holes through them, and the plywood. Then put a screw with a washer into the hole, and put a washer and nut on the other side to hold them together. One set of screws and washers for each hole. Seal the holes with a waterproof caulk, or something similar. Do this untill you have six sets of lids screwed together with the part that the bucket snaps into facing outward. Snap the buckets into the lids. Another method is to use duct tape. Simply tape the lids together. It works, but imho, not as well.

By now you have three 2X4's each with a set of buckets on each end. Using duct tape, tape the bottoms of the buckets together, until you have six buckets in a row. This is one pontoon. Make the other side the same way.

Next, attach the nylon straps, with screws, one each, to each end of the 4 ft. 2X4's. Wrap the strap around one of the buckets (near to, but NOT to the lid). Do the same for the other side. Do this for each of the six sets of buckets you have. An 8' strap will go around both buckets.

Now attach the 2X2's to each side of the 2X4's, then simply place the plywood on top of it all, and screw it down.
Maybe not up to Navy specs, but this thing can be used as a boat, a raft for the kids to play with, enough of them can be used as either a emergency dock, or a pontoon bridge, depending on how you put them together."

A little small for matching animals two-by-two onto, but sounds like it would work...