The three who look their keys opened up their chosen caskets and found that they all contained a basic set of utility items:

100 credits (around £100)
A com system connected to each other for communicating at a distant
A watch counting down to a specific date (which would appear, in real world terms, to be the same day as Midnight GMT on the 30th of April)

Each container also contains one other item:

Eudial's casket contains a blood stained knife that appears to be a powerful charged battery of magic, albeit of a kind that causes her skin to itch. It would seem to be of a holy nature so using this energy would presumably be super effective against any sort of unholy things.

Leland Gaunt finds that his container contains a waistcoat, which seems to grant immunity to any level of cold you could find on earth, and also seems to have a finely made telescopic harpoon hidden in an inner pocket along with a number of tiny marble sized smoke bombs.

As Twitches casket opens it initially seems to contain a huge skull of a Marowack which must weigh as much as Twitch himself, however, even as he looks at it, it reforms into a far smaller helmet that would fit as a helmet on his own head, and seems impossibly hard.