ORIGINAL: Rob/PA Bowyer
If you take only one call to the woods your missing out on birds. Some birds respond to one call and not another. I've walked through blocks of woods with one call only to switch it up and get responses behind me that didn't talk to the previous call.
Pick yourself up a box call, slate/glass call, push/pull button box and learn the mouth call. One might work when the other doesn't.
that's very good advice. I'll only add if you're huntin' in the spring, get a crow call and an owl hooter.