So really, how do brick and mortar merchants accept bitcoin payments in 1 second or less without risking double spending? Do we actually have a solution for that which doesn't require me (and merchant) to use a proprietary bitcoin app but let's me use a generic wallet app?
I wouldn't be surprised, but haven't checked, if Coinbase or somebody has a solution for this, but I'm guessing it requires both merchant and customer to be using Coinbase.
I guess if the larger bitcoin firms like Bitpay, Coinbase, etc provide guarantees to merchants that the transaction will be confirmed and they take the risk of fraud (double spending attacks) then that is certainly one solution. They can quickly (1 second?) do a check to make sure transactions look ok (based on current blockchain) and hope that double spending attacks will be rare.
Coinbase and eGifter facilitate your ability to purchase groceries quite nicely. Coinbase is a place that lets people easily acquire BTC, and eGifter is working to let people spend it basically anywhere, even in places where the merchants don't know about BTC. Let's assume you have the eGifter app and a Coinbase account, and need to buy $200 worth of groceries.
1.) Shop for some food at Walmart.
2.) You can buy a walmart giftcard straight from the eGifter App using bitcoin.
3.) Egifter gives you a whopping 6% discount, which means you paid $188 for your $200 Walmart Giftcard. (why can they do this? Because BTC doesn't charge back)