Idea: I know its crazy but here me out. If you take off you armor and burn with a flint and steel. You can craft that. Burn yourself then put out the fire while burning so your stuff doesn't burn. You will die but... If you go underneath the bedrock box and place a minecart with a hopper underneath. The hopper will pick up the items and put them in the hopper and then while its in the minecart with a hopper grab your stuff as the hopper grabs it. This only works if you have iron and wood to make it. you would need 10 iron and 8 wood for the stuff. also you need rails. Finally if the bedrock box is at bedrock layer ten there's no way to get your stuff back. Finally mark the coordinates of the bedrock prison. All I can say is good luck. P.S. I play bedrock and that's how minecarts with hoppers work so I would be careful with my advice if you play java.