Dropping a phone in the toilet:
There’s no such thing as true prevention here, so focus on preparation. Immediately yank it back out of the toilet. If possible, immediately remove the battery without stopping to shut down (if not, just immediately power off). If there was anything but water involved, rinse the phone with fresh water. Take the phone apart as much as possible before putting it somewhere to dry for three days, and covering it in rice might help wick away moisture—yeah, seriously. Of course, there are always waterproof cases to prevent this catastrophe in the first place.
Losing a wallet: While it’s inconvenient, losing a wallet is not the end of the world. These days almost everything in a wallet is replaceable (if not, take it out of that wallet now — including a social security card). When in public, allow 15 minutes to calmly retrace steps and search for the wallet (at home, allow an hour). Then start canceling credit cards. Make a list of account numbers and associated phone numbers to keep safely at home, along with contact info for the DMV.