Trying to make sure I have right terminology on it - and we have slightly different names for things, and sometimes different stuff, here over the water:
Personal id stuff - birth certs, (baptism certs), marriage certs, passports etc
School, college, other certs of courses and qualifications etc
Medical history stuff -Dr names, vaccnination records, any notes of procedures/allergies/bloodgroups if known etc (just highlights of med history really), drugs payment scheme cards, copy of an old prescription (I have inhalers I need)
Important tax etc stuff - P60s, P45s, tax certs, social security no.s (National Insurance? We have PPS nos here),
House stuff - mortgage holder details, annual mortgage statement, solicitor details, any major works done/defects identified/surveys carried out...
Car registration details - log book, MOT history etc
Utility account nos
Bank account details - current, credit card, savings etc
Any other savings/shares - certs if have them, just a note of what we have
Insurances - health, house, car, life, mortgage cover, travel etc
List of emergency contact numbers and emails (major family members, reliable friends, school, creche, work, etc)
[Receipts for "big ticket" items have a spot too - although not in the emergency grabbable box]
I also keep our loyalty cards for the various travel/hotel groups there too