You guys should spit into empty water bottles. The only problem I've found with this method is that if you're really in a bad coughing fit, sometimes your spit is larger than the top of the bottle or you miss. Thats unusual though. Its also fun to watch it slide down the side of the bottle. That's a great way to tell how sticky it is. Somedays it goes right down and others it gets stuck on the side and may take over an hour to fall down.
The best thing about spitting in bottles is that you have top and can re-use them a few times. I normally get them 1/3 full (16 oz) bottle and then toss em in the trash. Tissues got too messy and I was using way to many and always had them sitting around. Spitting in something without a top grossed me out. It won't spill if its in a water bottle. Its funny after a while, the mucus separates from the water and sits on the bottom of the bottle. Very weird. Almost looks like sand.