Items that would go in your suitcase or hand luggage.

Medication

Passport.

Secret socks - specially-bought ones that are designed to stay on the foot.
Trouble is, I am on holiday now but those socks are not - they seem to have unpacked themselves and stayed at home. I definitely put them in the case!

Toiletry bag

When absentdaughter gave us very short notice that she was getting married in New Zealand, it was quite a panic to arrange to get there. We had trouble finding available flights because I had to finish a freelance work project before leaving at the very last minute. We bought wedding presents and family and various friends passed presents over to us to transport. For reasons of space, we had a carry-on bag packed with small kitchen items– a selection of sieves, a potato peeler, a pizza cutter, a decent can opener, etc. That bag went through X-ray umpteen times with every officer in the place twisting their heads around to try to work out whether that was some kind of hugely advanced weapon. None of it was helped by the fact that even when absenthusband was stripped down to his underpants, he still set off the alarms. I really thought I would have to leave him and half the presents behind and just fly to New Zealand alone.

As it was, the flight had all sorts of problems and delays and one suitcase with most of my knickers and my wedding outfit finished up in Sydney.

Pashmina

Various glues, mending tapes and sewing kit. Usually lent to others on holiday!

Hot hair brush
Suction Sting remover.

DH has multi use penknife in suitcase and is never without tape.
Over the years he has made many a quick repair for ourselves and others

Clothes and toiletries everything else goes in the hand luggage in case the suitcase gets lost . Cynical Moi?

My little alarm clock. It always travels with me, in my hand luggage.

Prescription meds

Change of clothes in case suitcase delayed. Toothbrush and paste.

Always make sure that essential medication is in hand luggage. (Oh, and a pair of knickers! Priceless if you are grounded for a night because the plane can't fly in bad weather... This did happen to us....)

Oops. I thought as this was in the Games threads, it was meant to be, as usual, one word answers.
I have been needlessly racking my brains to think of single items.

Holiday cash.

Keep up Mary ?

Mini pillow

My mum's travel clock, pills and panty liners

Notebook and pen