I've flown out of SBN with a SkyTrain from Red Oxx. They made me gate check once, ExpressJet/United. Kinda pissed me off, since I was able to fly into SBN on SkyWest without any pushback. Both were CRJ-200's. My Skytrain will fit overhead and under the seat.
For your packing, ditch the jeans, cut down on the tee shirt, socks and underwear. Sink wash the delicates. Buy quick dry, technical fabrics. Go as light as you can.
And get Global Entry/PreCheck.