So at my full time service EVERYTHING gets checked out. There is one 24 hour paid guy on per day, and 3 day shift paid guys. These 4 are responsible for checking EVERYTHING in regards to supplies each day. There are some weekly checks like oil level, coolant level, Fire Extinguisher, Gun Safe, etc. but medical supplies are daily. This mean number of supplies, as well as every single intubation blade's bulb. Since they have 2 trucks to check plus the back up truck, truck checks each day take over an hour. It can be done in just shy of an hour if the 5th man on duty (a volunteer) helps out.
The only things that are sealed are the pediatric broslow kit, and the drug kits. All the seals are signed for, so in the event a drug kit is not stocked correctly, we will know exactly who fouled up. If it must be resealed without being full, then a note is left in the seal logbook, in the station notes for the oncoming crew, and a note is taped to a full 8.5x11 sheet of paper across the front of the box such that whomever is doing the next truck check is able to see immediately that there is a varience in the drug kit.
The only reason we seal the broslow kit is for convinience--it's rarely used and checking three of them daily would add another 30 minutes to the truck check time. Also, once a Broslow kit is used, it's done. We take it out of service and grab a new one off the cabinet. The full-timer ordering supplies will go through it using a checklist the company provides, send in the completed checklist with missing parts, and they send us the replacements before it gets sealed again.
The only reason we seal the drug kits is to keep track of who used them. Since any of our trucks can be a squad, advanced squad, or medic on any given run, we need to keep the basic drugs separate from the intermediate drugs, from the medic drugs.
Also, because after 4pm, only one full-time staff mamber is on, this means the rest of the crews can be responding from home. If that is the case, they need to know their truck is checked out and ready to go.
So I guess the take home message of this is: if you have highly trained people checking out the truck each day then the chance of error is slim. Does it happen still? yes. But at some point, yo got to learn to trust the guys you with to a certain extent. If we checked out our own trucks before every run at night, you'd be waiting a long time to get help...