Continuity mistake: After Rey finishes her meal beside the foot of the AT-AT and puts on the Rebel flight helmet, there's an overhead wide shot of the toppled AT-AT and we can see its front knee joint. When Rey hears the commotion with BB-8 she rushes to get her staff, which is now tall and upright in the sand at that knee joint, and had her staff been there in the wide shot we would have seen it.
Picture added by Super Grover
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