This would allow the wristband to be reused at future events, even with a different merchant.
I can't help but think that there's a place for RFID wristbands in providing a wallet that is both convenient and provides financial privacy.
Here's Kashmir Hill's article on Disney using RFID wristbands:
Of course, those from Disney are not providing financial privacy but quite the opposite -- full personally identifiable tracking.
From just a little research on these, I've learned that the advantage of using these bands to the event operator is that they are a faster payment method than cash or card, and there is much less pilfering than occurs with cash transactions (which, with events that hire local, temporary help has been an issue in the past). One advantage to the user is the ability to convert cash brought to the event into value stored on the wristband and then not have to carry any other electronics or cash (which would require a wallet, purse, side pack, etc.)
Here's one approach (if financial privacy isn't a factor):
Coinbase, a hybrid E-Wallet, now has "subscriptions". This is essentially a pre-authorization (authorization for future spending).
So then let's say I am going to Coachella music festival. I sign up on their site and it sends me to a Coinbase login where I am asked to authorize a subscription allowing $100 per-day of charges against my Coachella wristband. I don't actually need to have $100 worth of BTC in my account when authorizing this, I am simply giving Coachella my permission to pull up to $100 a day for purchases.
So I then click authorize and later on the wristband from Coachella arrives in the mail. I confirm that I received it so that it can be used at Coachella. Now I just make sure I have a sufficient amount of BTC funds at Coinbase and I can go to the event. I don't need to bring an ID, smartphone, wallet, etc., ... I just wear my RFID wristband that Coachella sent to me.
If I lose the wristband, then if I have my smartphone I can then cancel the subscription or else I can notify Coachella who then will block any further purchase attempts for that wristband (there are protections available to prevent griefers from cancelling other people's wristbands, like asking the amount of the authorization, or amounts of previous purchases maybe, etc.) Adding more funds to a wristband (or getting a new wristband after losing one) will require bitcoins (at coinbase, or in some other wallet), or cash or good friends, so a wristband doesn't solve every problem for everyone.
But the above approach requires this subscription capability from a Coinbase or other E-Wallet provider -- and the event operator then knows my Coinbase e-mail address from my purchase.
What is interesting is the ability for the RFID code to simply be just one of keys for a multi-factor transaction authentication. Perhaps instead of using a subscription service would be to take advantage of Bitcoin's ability to require M-of-N keys, or some solution using Shamir's secret sharing service from Vitalik Buterin's btckeysplit tool perhaps. The RFID code, being a static value, is something that is vulnerable to a replay attack and that limits its usefulness. A TOTP code, like a Yubikey wristband, might be more useful but then it is no longer a $4 device.
The problem being solved is that today these wristbands work fantastically as a "wallet" for events, but they are not offered at many events (as a wallet). Presumably this is for the same reason as any other financial innovation gets blocked ... regulatory capture of the payments industry through money transmitter laws.
But Bitcoin provides a path where this concept (wristband wallets) could become used.