The marriage supper is simply a 'get together' after the ordeal of life on earth and Christ's judgement. It is a reward in the sense of being able to sit around with Christ and just relax. There is nothing in the Bible to suggest it is not a real supper or meal. Although we will be spiritual creatures, and by implication, not needing food, it is described as a supper, therefore we must assume there will be food of some description.
What ever the content of the supper it will be a time of contemplation and looking forward to the next phase of eternity. A supper in earthly terms is a winding down a relaxant or time of regeneration before the coming morning and a new day.
After the total change of environment and physical persona we will undergo, the idea of a supper is one of normality, something to bring us 'back to earth'. Obviously no one will suffer from shock at the changes taking place but it is as if God adds a bit of humanity to the proceedings to keep the shock level to a minimum. Familiarity has a great calming effect during times of stress or change, also a meal as a family is a great leveler, as in the last supper, Jesus reclined with his followers and served them.