I agree, love the boats idea.

If its about a matter of time, and choosing which to put in first.

Carts (slow for carrying heavy stuff)
Wagons (semi slow to carry people and stuff with animals)
Boats (barge types, slow carries a lot)
Mounts (fast, or pack mules)
Fast small boats.

In that order of need. I would also like to see ranged weapons working in game before we see fast mounts and fast boats.