It would be nice to have curtains that absorb street noise.
Some custom curtain tailors offer a fabric that claims to be soundproof. It’s a little pricey. Not absurdly pricey, but it’s also a bit hard to be confident that such thin fabrics can absorb much sound (they claim 20%).
I would prefer to try hacks. I’ve heard that thick furniture moving pads absorb sound well. I’ve also heard that fiberous fabrics can be effective. For the moment, I probably want to pass on edgy ideas like egg cartons. Maybe later on those. What fabrics are decent for reducing sound? Specifically, I’m wondering about carpets or painter’s drop cloths. Not the simple white canvas drop cloths, but the thicker drop cloths may out of recycled fabrics.
Sound absorbing materials with some space between them will work best, so if you go with curtains you'll want to get the double curtain rod to put in two sets. The space between the material helps reduce the transfer of sound energy.
White noise machines do wonders for killing external noise, but then that's all you hear. Similar to running a loud fan, I can't hear anything when my fan is running.