i would suggest that you find out his diet plan .
go home and clean out the kitchen of all the no no foods. throw them away or donate to a food cupboard.
buy some small plates ( saucer sized.)
baby spoons He will have to eat slowly
an insulated lunch bag HE will probably have to carry his own food for a while.
he will need some reusable ice packe to go with that.
look up recipe websites to learn how to cook for the surgery patient.
start buying the vitamins as they go on sale.
some helpful websites
you can find the older topics on the episode list
just search the type of wls you need
good luck. maybe you could find and attend a local support group together. some also have support for supporters and family.