Rent bikes or scooters (the latter, it must be noted, are frowned upon by locals) at Nantucket Bike Shop (with two locations on Steamboat Wharf and Straight Wharf, 508/228-1999, www.nantucketbikeshop.com [1]). Or, if you’d rather have the wheels come to you, give Easy Riders (508/325-2722, www.easyridersbikerentals.com [2]) a call. The warehouse-based operation has reasonable rates, all kinds of bikes, and free delivery to wherever you like around the island.
Links:
[1] http://www.nantucketbikeshop.com
[2] http://www.easyridersbikerentals.com