The annual gear review is a terrific idea, and something I've done every year for a long time. (Well, most years...)

There's also a similar hazard when you decide to upgrade or replace something. You need to make sure that you have all the little auxiliary stuff to go along with it, and that it all works together.

For example, I'd been using Platypus bags with the Sawyer filter, back when it first came out. The bags wore out a couple years later, so I bought some replacements and tossed them into the pack. When I went to filter water, I connected the bags and water gushed out the connections, all over the filter. I didn't connect the new bags before the trip, and didn't realize that Platypus had changed their bottles, just a tiny bit, so they weren't compatible with the Sawyer.

Likewise, when I realized my headlamp was shot, I replaced it. A few trips later, when the batteries played out, I grabbed the spares - to discover that the 3 AAA batteries (old lamp) didn't fit into the 2 2032 coin cells the new one used. Luckily, the moon was full.

Sometimes, you need replacement stuff to go with the replacement stuff.