Going to a first class airline lounge doesn't necessarily exclude you from doing all this. Especially if you fly domestically. Some airlines don't have a first class, and rather a business class, so no lounge. Most of the lounges you refer to are international, because they're longer flights (hence why they are referred to as Long Haul flights) or they have a very, very good first class. Lounges do not exclude you from checking in, checking baggage, and you security check, because the SC is through TSA.