This is a post card on ebay that the seller says is Squirrel. The url is Click here
Or if you know ebay you can look up Squirrel Island or item number 6175638649

Barbara Rumsey at Boothbay Historical has added the following:

I think the girl (there's another pic of her in our new picture book) may be a Sockabesin who were stationed near the footbridge

Taken from Oct 2003 piece: Next right is the Harold W. Bishop house at the east end of the footbridge, now Steve Branch. Harold provided space for many years for the basket-selling Indians, the Sockabasins, who came from Old Town in the summer. The Bishops adopted Ann, one of the Sockabasin girls born about 1918. Virginia Gamage stayed at the house in the early 1920s to help out when Harold was away. Ann, a preschooler, would come and get in bed with her--just as my children used to with me.

The truck is reminiscent of Claude Miller's milk truck; but his is boxier. The Railway Village has it, I think. But maybe their Miller truck is a later version than the one I have a pic of. If you want to keep searching, maybe send a pic to the Village.

Here is a scan of the page from Barbara's book and the text, a little more readable is below. Clearly the picture and the post card below of the little girl were taken on the same day.

The text on the image above says:

From the beginning of the tourist era in the 1870s, families of American Indians, including the Rancos and Sockabasins, came to Boothbay in the summer to sell their wares, principally baskets. Also popular were "war clubs," made from alder roots, carved paddles, and snowshoes, as seen in the above photograph. Normally, the families came from the Indian Island reservation at Old Town. Above, the Sockabasin tent, once a familiar sight, appears at the east end of the footbridge in Boothbay Harbor c. 1915. The family stayed at that location for many years, occupying Harold W. Bishop's lawn, and Bishop adopted one of the children. Below, a Sockabasin girl sits in a basket for the camera.

There are my original thoughts and the post cards are below:

So what do we think? It is on a paved road? so it can't be Squirrel? The seller says that could be smooth dirt. The buildings are all wrong. The windows have storm windows on them? The truck is packed for a trip but you can't go far on Squirrel. Are the cans on the running boards gas? What are the things that look like wooden blocks in the foreground? Could this be in Boothbay before being put on a barge to Squirrel? The truck is so heavily laden. No one in their right mind would drive a truck with a heavy load on Squirrel's rutted roads. What about the road from Wiscassett? Could he have gone to get more stuff? It would be dumb to take a heavy loaded truck on a barge, right? Driving on and off the barge is the worest time of all! The seller says the name connected with the truck is Arther? Grant. That was the store owner. The seller says it came from the same place as a picture that we do believe to be connected to Squirrel, the Indian girl, posing with bow and arrow. I have put it below also.