What can I use to replace transmission fluid one time in case of emergency
What ever the manual tells you. Or any parts store should be able to look that up.
If you’re worried about a transmission emergency then why not carry a couple of jugs all the time? Stick them behind the seats along with a jug of engine coolant and maybe a quart of motor oil.
ATF+4 , any brand
If this is an automatic transmission, use only licensed ATF+4. Do not use any of the so-called “universal” transmission fluids–they will ruin your transmission. Wal-Mart sells their SuperTech brand for about $5 per bottle, which is a very good deal.