Slightly interesting glitch: A variation of what Oreo posted can be done on a lot of levels by getting into the box while falling just before it burns up. The easiest level is level 3 by just holding left and down while pushing the box into the fire. To do it on for example level 4 (and many other levels), just push the box off the side, wait a bit, jump off above it and hold down. If you got the timing right you'll be put in the box while it's burning up and the glitch is done.
This glitch is interesting because while you're in this state, if you hold up and release you'll jump higher than usual (while not in a box) which could possibly be used for something in the future.
Was going to post this a couple weeks ago but forgot /:
More useless glitches: On level 9, place one box on the other but slighty to the side, get inside the lower box, try to walk away from the box above you and spam jump at the same time. If you did that correctly you'll get stuck in the side of the box above, here you can press down to get in said box and lastly jump out of it. Both boxes are now completely stuck. Another interesting thing about this is that if you get in the box on top and press either right or left you'll be put in the box below.