I'm hard on engagement rings; well, the first was actually a "promise" ring.
Ring #1: We were driving cross-country in the summer in a compact car with no a/c. I was driving and took my green topaz ring off, set it in the lap of my skirt. Stopped to get gas, hopped out, pumped, went on our way. About an hour down the road I realized I wasn't wearing my ring. We back-tracked and there it was; someone had set it on top of the gas pump! It was a little "crunched" but it was silver so the jeweler easily formed it back into shape.
Ring #2: Amethyst with diamond chips. I was working all day setting up a dinner/performance fundraiser. I was changing in the dressing room (into my big-kid evening clothes) and took off my ring to put on pantyhose. Didn't want to snag them. Totally forgot to put the ring back on and never saw it again.
Oddly enough, the building we were in underwent renovations to become faculty office spaces. Three years after I lost my ring, that space was assigned to my husband as his office!
Ring #3: Center diamond (1/3 carat) with ruby side stones. Hot summer in MI and I was pregnant, with swelling feet and fingers. I took my ring off somewhere while doing errands and never saw it again. I'm still pretty sure that I put it in my shorts pocket (slash pockets) and it fell out in the car- the one my FIL vacuumed that evening, but I didn't realize the ring was gone for a little bit. It was either that or I put it in my change purse and took it out when paying for something (back in the day when people actually carried cash/change).
Ring #4 is three garnets with diamond side-chips. It's on my left hand. If I take it off, it goes on a toe, between my lips, or in a ring dish, depending on where I am and what I'm doing!!
ETA: I just remembered- I left my Disney VISA card at the gas station across from the Boardwalk Inn. We stopped to get cold drinks on our way to BWI, where we changed and then went to dinner at Boma. That's when I discovered my card was missing, but I knew right where it was. We took the bus back to BWI but it was late, so I decided to wait until the next morning to get my card. SURPRISE!! Not only was the gas station closed, but there was chain-link fencing up around the lot and they were pulling up the underground tanks! Called Chase and they were great, canceled it and offered to overnight a new card (but we had a back-up with us), etc.