If you are looking for caps for those "BERTY" tubes. I have found this "HONEY HOLE" where you may find a bunch.
If there are no games going on, the dugouts are good places,
If not, check the trash cans near the grandstands.
Just search the trash cans for empty Gatorade (20oz) bottles, Powerade (any size), Minute Maid bottles, Borden (pint size) milk bottles and other bottles of the same size.
As for the cache - you may have to reach up to retrieve the BERTY tube. Plenty of parking is available. Muggles may be around the area.