Two things:

I found out the hard way that old boots sometimes need to be replaced. Went for a little 2k walk the other day and got a blister -- which never happens. The culprit, cheap socks and a small hole on the inside of the boot. Why makde me think -- its about 6 mo past time to get new boots.

Another tip. I replace gear all year, spreading the cost out. Replace meds at the start of the hiking season (spring), adding some gear as I find it* and saving up for big gear.

Keep thosse kits current!

Teacher

(* I have found tons of almost new gear at second hand shops; fleece, water bottles, day packs, etc.)

I check all of my gear (including FAK's, fire-exthinguishers,flashlights) when the batteries of the smoke-detectors need replacement, or after use.
('Preparedness-Day' )

My hiking-kit, house FAK and EDC are used more frequently, so they are checked more often.

As for the costs: I have to replace water-purification and food-rations only once every 5 years, so not much costs here. Bottled water is replaced from the tab meaning no expenses for me. (but for my parents ) The only thing that I need to replace frequently are batteries and FAK-supplies.

The only thing that worried me where the starting-costs I made to put this gear all together, not really the costs of maintaining it.

BTW: if for example the TV-remote bateries are empty, I take the batteries out of a flashlight or radio and put new in the flashlight. That way I know for sure that my emergency-gear has fresh batteries.

I used to set reminders on my calendar but would always get tired of snoozing a dozen reminders until I had time to do anything.
I sat down last last year and made a spreadsheet with weekly, monthly, yearly, etc lines and different maintenance items to check. From recharging or replacing batteries to buying extra flashlights. That way I can check off that I did my "maintenance" when the time is best for me and have a log through out the year.