If they didn't have an enemy in the world, even then some tramp could come along and clean out the camp.

Humph! Two tramps, if they wanted to work for a little while, could carry away all the food there is here.
What a lot of poor, penniless muckers Prescott and his friends are!" Again Fred studied the lay of the land, then drew off his coat and flung it aside.
"Now, to work!" he said to himself gleefully.
First of all, he got the food supplies all together.

Most of this stuff was in the form of canned goods.

Ripley gathered it up in one big pile.
Then he stepped over to the tent, from which, at several points and angles he looked carefully over to the hotel landing float on the other side of Lake Pleasant.
"They can't see, from the hotel, whether the tent is down or up," Fred determined.

"So here goes!" Opening the largest blade of his pocketknife, Fred cut one of the guy-ropes.