This is so individual. Think about what they love for birthdays or simchos and use that as your guide for the types of things they find helpful. Some quick suggestions:
Invite for an hour out
Text them before Yom Tov
Check in Motzoei Yom Tov
Drop off a little feel-good something
If hosting children, find out their food preferences or favorite toys and have them on hand
When hosting a grieving family for the Seder, hand out matzah or maror by age and not by family
