I've just thought about this...if you are on blood thinners now, can you start noting the color of the blood they draw from you for blood thinner levels?...like have them place a tiny drop on your finger, and see if after time you can guess what your numbers are going to be...like if you blood is very dark, or very light or seems think of thin....perhaps in a SHTF scenario, you could develop your own way of determing your dose....
A less risky course might be a supply of ground cinnamon. It contains some coumadin (the active ingredient) and a regular intake of 1/4 to 1/2 tsp cinnamon per day will have a measureable blood-thinning effect.