I second the FoodSaver suggestion but since it's only a day you're looking at whatever is handy will do.
You have a choice: Slice after its rest, store the slices, and re-heat the day of, or store the whole brisket and re-heat it the day of. Brisket dries out fairly quickly after slicing but the re-heating time is less. Whole brisket will store better.
If you choose to slice after resting and before storing save any juices that have accumulated in the foil. Slice your brisket, store in a FoodSaver bag or Ziploc and add those juices to the bag. (You don't need a lot of juice, but if you need to store in several bags say, and you don't have enough juice, add a little beef stock or a touch of apple juice.) Re-heat the slices with the juice in a pan tightly covered with foil in a slow (250) oven. Check them in 12-15 min, then every few minutes thereafter. You want the slices to heat well but not cook, which would give you pot roast (sort of).
If you go the whole route, rest your brisket as usual for an hour or so then put it open the foil from the top. Leave the brisket in the foil (and leave those juices!); put the whole thing in the fridge still open (if you have solid fridge shelves put it on a cookie cooling rack first to allow air to circulate under it); this will allow it to cool more quickly. When cool, close and seal the foil. To reheat: remove the brisket from the foil and put it and its juices in a pan then tightly cover with foil. Put it in a 300 oven; check it after 30 min and every 5 min thereafter till hot. Slice; serve; have a great time.