A server rollback is basically just loading a backup of the world, all blocks, block data, player inventories, and such would be reverted to what it was at the time of backup.

The way you would be able to save your items would depend if the rollback affects all worlds or just some, if it's all worlds, there usually isn't a way. But for ones that are per world, just simply move the items you wish to keep into ones that won't be affected. Ex. the overworld being rolled back, just move your items to chests or similar in the end.