I simply keep an eye on straps. On the Dakine sliding bar, I used to flip it around, move it to the side, to even out the wear until I feel like it's time to change the strap. On non-sliding harnesses, straps still tend to tear a little, you may went to vary tightening to spread the wear or just go with the rule that once you have 1/2 past the original thickness of the strap, change it. Similar to harness lines.
Hooks may crack which gets larger little by little, or the hood just breaks in half leaving enough strength to head back anyway.
Helmets? I used to run a plastic pro-tec, it was too large, too much slap from the water, headaches.
Maybe some soft padded helmet such as this one:
What type of protection are you looking for? (against foils? other riders? your own gear? natural obstacles?) I got bumps on my head and cuts to my face, ice and superglue or steril-strips are still cheaper and more convenient than helmets :D !