You can drop as many trips as the reserve coverage will allow which has been very few the last three years I've worked here. Once the reserves available are equal to the reserves required you cannot drop a trip. That usually happens within a few runs of the initial PCS runs where guys start dropping and swapping trips each month. Some months and some categories might allow more drops, but I would be surprised if you could drop all of your trips very often.

A white slip is a request to pick up a trip on your days off if your a lineholder for normal pay. A green slip is a request to work if they need you on your days off for double pay as a lineholder or straight pay above guarantee as a reserve guy. You will get a white slip trip before if goes to a reserve guy and you will get a green slip trip only if they have no reserves left. The contract lists the priority of trip assignment for both a GS or a WS request.