I recently had to get very creative. I was in the middle of a 250-plus-mile road trip, just me and my daughter and our dog, when I had to go to the bathroom. I didn't want to carry the car seat into the bathroom with us, so I put her in her baby carrier and went to the bathroom with her like that, essentially sitting on my lap. It was weird, unusual, and, I'm guessing, one of the many things on-the-go parents come up with when strapped for time.
I wish I'd had the TushBaby Baby Carrier ($80) with me. Unlike traditional baby carriers where the child is completely strapped in like they're on a swing or amusement park ride, the TushBaby is more of an unrestricted seat. It's super easy to get them in and out (or on and off, rather), and it takes the weight off your arms and lower back. The belt fastens in a breeze, and you can place baby facing you or facing out. There are also pockets so you can store diapers, wipes, and anything else you might need. If you find baby carriers bulky and constricting, you'll definitely want to try this out.