Both UPS and Fedex have it on their website that you can print a label and pay on the website. Then drop it off at their store, or have it picked up. I have never been asked the contents.
Same here - Neither UPS or FedEx ever asks me about contents as long as I pre-pay and print and attach the label at home. It's a very simple drop-off process at that point. In the very unlikely event that they ask, just tell them it's non-perishable food, glass/fragile, so be kind of careful with it, etc.
It's also important when packing it, if you haven't done this before, to line your box with a big garbage bag and put everything inside that bag and tie it up. Then if there are any bottle cracks or cap leaks (both of which occasionally DO happen unfortunately), it won't soak into the outer cardboard and cause them to question the contents en route. They should have no reason to question a well packed box unless they totally mutilate the box, and then that's THEIR fault, not yours.