Unlike polymorph, druids have the option which magic items merge with their body, and which ones are still worn (assuming their body shape could conceivably wear an item of that type).
Worn items resize to fit the wielder (as stated in the DMG)- a belt is just a loop of leather with a clasp (as a rule, although fancier belts might be made of metal or have decorative attachments). Assuming size is correct, you can fit a belt around a dog's waist just as easily you can a humans. It won't serve much practical purpose for a dog (magic not withstanding), but there is nothing stopping them from wearing one. Yes, worn items don't reshape to fit the wielder, so armor/boots/gloves are problematic for non-humanoid forms, but something like a belt, ring, cloak, necklace or even bracers (which are just metal/leather cylinders for the most part) should work on most wildshape forms.
Take a Giant Elk for example - Bracers of armor or a giant strength belt should still work on its forelimbs; athough they would scale in size to fit. With that being said, a giant elk doesn't have anything similar to "fingers" so wouldn't be able to wear rings (as magic items don't relocate to different locations when wildshaping).
Meanwhile a giant snake would only be able to wear something like a belt, as even cloaks/necklaces would have no physical equivalent of "shoulders" to support them, while a belt can be simply tightened around any cylindrical body part (including a snakes midsection). A whale on the other hand would have trouble with bracers as their forelimbs are flattened instead of round.