radeng I understand your concerns here as I'm a nurse so know how important this would be for you.
My advice, and it's purely the advice of LCD not any official airline protocol, is to carry what you need including your wallet in a bum bag.
Some of the larger ones can obstruct the seatbelt so if that is the case shove it in the seatpocket in front of you where it is easily grabbed in a hurry to leave. No CC would stop you carrying this down the escape slide.
Hope that helps
PS on a nice normal flight don't be the one who leaves their personal belongings in the seatpocket in front of you after I've just done the PA telling you not to do this.....the paperwork would be endless
