The Comfort Stations have machines that dispense a bag for $2 in quarters (change machine in the laundry room between the men's and women's shower rooms).
The Trading Posts also sell it for the same price I believe.
The ice from the CS is kind of slushy; also bring a second bag or cooler, it often dispenses more than will fit in the bag. Second the vote for the Hess station, it's cheaper.
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