Need travel advice!

Okay mama's,  my husband & I will be traveling with our 4month old (will be just shy of 5months) in 3 weeks.  We're going to hold him on our lap on the plane,  I plan on using my sling.  What's the best travel products or tips you have?  This will be our first trip with him.   Curious about car seat/stroller check ins,  do we do at the gate? Or ticketing with our luggage!  Any advice is greatly appreciated!