A thing I'm glad I had on my recent trip: a filter wrench. My wife picked up my camera bag, which was unzipped, and out fell my 24-70 with a B+W CPL attached. Made the threads go wonky and I couldn't unscrew the filter from the lens. Luckily I had a cheap little filter wrench in the bag and managed to get it off. No harm, no foul.
A thing I had, and lost, and miss: Remote cord. I used the tripod a lot on this trip, and always used a remote shutter release. Two days before we headed home, I lost the cord. Using the camera timer sucked! Trying to take pictures of my wife and I at Lovers Point in Pacific Grove I had to hit the 10 sec timer, then scramble over uneven rough granite to get to my spot. Many attempts, a couple of which worked out okay. The others... I fell over twice trying to quickly sit on a rock next to her, twice more scraped up my leg on the rocks, and didn't make it in time for a few other shots. I ordered another cord the day I got home. I'm too old for that crap.