For low value transactions (like a cup of coffee), you could take a risk and go ahead with unconfirmed transactions. It is highly unlikely they will be double spent. For high value transactions, you can wait for 6 confirmations (or almost an hour)
In a great majority of retail situations, shoplifting, bad checks, dine-and-dash are all orders of magnitude worse than Bitcoin double spending, even if Bitcoin is used equally frequently. Aside from instant payment processors, double spends can be mitigated by simply banning specific humans from the premises of a physical store.