Without CASS you are excluded from the flight deck. Without a reciprocal agreement, you're out of luck except for a few who do offer "J/S privileges" for open seats in the main cabin. Last I heard, Southwest and Jetblue offered unlimited seats to 135 pilots. Call Res to list and check loads, then check with the ticket counter or gate agent. Last, but not least, when given a seat by the agent, stop at the flight deck and check in with the crew. Have your current badge, license, and medical ready, (In my experience about 50% want to look at my credentials) say something to the effect of "Hi, I'm Joe Pilot from XYZ Air, I'd like to ask for a ride; the girls at the gate have already given me a seat in back."
Best of luck!