There are many mamarei chazal that discuss things that at one point existed and were hidden or saved for "l'atid lavo" (ex the ohr haganuz) does an extensive list of such things exist?
I recall learning that la'asid lavo the trees themselves will be edible (ta'm ha'etz k'tam hapri) as in gan eden. I cannot find the source for this though.
At the time of creation the sun and moon were the same size, they were called the large luminaries and the moon complained that two kings cant be the same size. There must have been some difference ...