Sorry to read about your family member and that this trip is so sudden hun.
This is what I did, hope it helps -
Carry on - depends a little bit on whether you're doing a day/night flight but
PJs
Sleeping bag
Cuddly
Dummies (and a dummy clip so you don't need to keep picking them up off the floor

)
Muslins/cloth flats
Perhaps a wee blanket, the aircon can be pretty cool!
Cloth books
Rattle/favourite toy
Feeds - I calculated how many bottles C would normally have over that period and then added 50% more than I needed. Formula in a dispenser to make it easier. A couple of jars of food and lots of spoons. Any favourite snacks (eg at 10m we took rice cakes and toddler cereal puffs)
Nappies and wipes - I took 1 nappy per 2hrs of the flight (didn't get through them all but better to have too many than not enough!)
Bum cream if you use it
Small bottle of hand sanitiser
Pamol and syringe (just in case!)
Teething poweder (also just in case)
Change of clothes for arrival
Baby carrier/sling is a lifesaver in the airport if you've got one. And a lightweight stroller will be easier if you have that option.
Big suitcase - if you're staying with family you'll be able to do washing fairly easily so don't go overboard with clothes ;)
PJs
woolly singlets
socks
extra sleeping bag
muslins
blanket, bedding from home
extra cuddly!
long pants
long sleeved onsies
tshirts
jumper
warm hat
sun hat
bowls, bottles, sippy cup, spoons
any favourite food
a few toys but not too many!
we took one tin of formula and one pack of nappies and planned to buy what we needed once we arrived.
HTH