Even if you're over the allowance on something, honesty is the best policy. From what you've said about your no-frills travel I doubt you'll go over the current dollar threshold ($1,000+?) but even if you buy a couple of bottles of duty-free alcohol in Amsterdam, you're unlikely to get charged duty coming into the US even though the limit is 1 liter per person. I regularly go over that limit (4 liters of scotch last time), report it on the form, and get waved through anyway.

And in case you haven't been through this drill before, remember that even though duty-free alcohol is delivered to you on the plane, when you get to your first port in the US, you HAVE to put it in your checked bags. They will not let you carry it on to your flight back to Birmingham.