Ok before I hit the hay. You can turn into an animal at will. Your clothes and such won’t turn with you but mass is not conserved so you can turn into something much bigger or smaller. It has to be a real creature that does or has existed and I guess if you want a plant that would be fair game. For me its an albatross. could travel around the world. might even manage to carry something that is not to large if packaged right. I am a bit torn though as the ocean is large so maybe a sea creature would be better. like a killer whale. of course then its not great for getting somewhere inland.
Hey OP, have you read the Animorphs book series? They’re a YA series, but it actually gets into some heavier shit surprisingly (child soldiers, PTSD, etc) and are not half bad. I bring this up because the premise is some teens are given powers to morph into any animal they “acquire” DNA from by touching. Really gets into the mindset of each animal, what it feels like, how awesome (or terrifying) it is being each animal, etc. Give them a read if you haven’t already.