I don't consider items like the Healing Belt and Artificers Monocle to be broken, per se, more of a drastic game design change. Whether that change is good or bad is debatable. Any item that provides an infinite-use of something that used to be single-use-at-significant-cost only has a huge impact on resource management.
If you're used to a game where resources are tightly managed - you keep track of all rations, spell components, and healing potions - these items give away something for free that used to be a significant cost. In that case, yes, they are broken beyond belief. OTOH, if you play a game where your DM never checks to see how much food you have and always just assumes you have whatever spell componenets you want, you may have been effectively playing with these items without knowing it. Puting them in the game will have almost no effect.
Personally, I think that both styles of play have merit, but some of these items really need to have a sidebar talking about them as optional items, and describing their effects on gameplay. They really have a greater effect on the game than some of the other "optional" rules listed in the DMG (auto-death on three natural 20s, for example). They're not the type of items you can throw into any game without regard to how they change playing style.
Any items that grant extra actions are right out. I thought we learned from that from the mistake of 3.0 Haste, but apparently WotC forgot. And that item (sorry, forget the name) that lets you go back in time is just plain stupid.