She was so busy wondering what Johnny was ordering, and why he was ordering it, that she had almost reached Sinkhole Camp before it occurred to her that Johnny had that unpleasant stranger with him, and that it might be awkward meeting the two of them without any real excuse.

Johnny himself knew enough not to expect any excuse for her behavior.

Strangers were different.
But she need not have worried, for the cabin was empty.

Since Johnny had not washed the dishes, Mary V observed that two persons had breakfasted.
She observed also that Johnny had been in so great a hurry to get that letter to the mail box ahead of the stage that he had unceremoniously pushed all the dishes to one side of the table to make space for writing.
She picked up a paper on which an address that matched the letter in the mail box and various items were scribbled, in a handwriting unlike Johnny's, and she studied those items curiously.

It was like a riddle.
She could not see what possible use Johnny could have for a quart of cabinet glue, for instance, or for a blowtorch, or soldering iron, or brass wire, or for any of the other things named in the list.