Might I suggest a middle ground? Go create a registry sometime soon, and include things you don't need to buy a ton of right away - bottles, onesies, bibs, toys, etc. Voila, options for people who want to buy you something specific but you can still do your own buying (which is half the fun of being pregnant anyway) and you can exercise more autonomy when it comes to choosing this car seat or that one. Then from now until the baby shower you can continue to stock up on whatever you want. After the shower you can pick up the last things you need.
Incidentally, some stores give you a % off anything on your baby registry after the baby is born - I think Target gives somewhere around 15% off at the 2-4-month mark. (Not sure on that - my memories from right after my two were born are kind of hazy!) So it's worth it to register sippy cups, a Bumbo, and other things you won't need with a newborn and you can stock up on them at good prices later on if you don't find them on sale first!