What, if anything should I take on a 3 hour road trip with a 3 month old?

Ok folks here’s my problem, my husband, know it all mom and I are going to visit my sister who lives 3 hours away. We are taking my beautiful 3 month old daughter who hates her child seat and has never been in it longer then 20 minutes. I know the basics to pack but I need tips on anything that can make this trip less painful.