Albert Barnes on Acts 12:8

Gird thyself. When they slept, the outer garment was thrown off, and the girdle with which they bound their inner garment, or tunic, was loosed. He was directed now to gird up that inner garment as they usually wore it; that is, to dress himself, and prepare to follow him.

Bind on thy sandals. Put on thy sandals--prepared to walk. Mt 3:11.

Cast thy garment about thee. The outer garment, that was thrown loosely around the shoulders. It was nearly square, and was laid aside when they slept, or worked, or ran. The direction was, that he should dress himself in his usual apparel. Mt 5:38-42.

(++) "garment" "mantle"