What can travel around the world while staying in a corner?

Is it more than you bargained for yet? I've been dying to feed you anything you wanna eat. 'Cause that's the food I am this week. Lie in your apps, next to the macro trackers. I'm just a snack on your cheat day, but you're just a diet gone wrong. Drop a carb. And break a fast. We're always sweetening it, and sweetening For the munchies.

I surround the castle, deep and wide, Keeping foes away with watery pride. What am I?

Notice me and see how I sit atop all the chaps, Guarding pates from sun's hot slap. With a brim so wide, or non-existent and narrow, I crown thee a stylish shield, so no need to bellow!

I jingle and clang, but I’m not a bell for your wrist. I wake the herd, yet I never insist. I sit on a neck, I’m loud in the field Guess who I am, my sound never yields?