Two things from me:
Immediately after my valve surgery, I took warfarin for the first 90 days. I kept a medication diary (still have it, but don't maintain it), and my wife supervised my medications. I am fairly certain I never missed a dose or over-dosed. Still, through the entire 90 days, the clinic never stabilized me within therapeutic range. Never did figure that one out. They tested 2-3 times/week, adjusted dosage, and still missed the target. My diet was stable, but my INR was not. I was glad to be able to stop warfarin.
Now, although I no longer take warfarin, I do take a lot of meds daily. My routine for the past few years has been that each evening I count that evening's meds and the next morning's meds into two cups. I place these cups on a shelf in my home office. Then, after supper, I take that day's evening meds. If there are NO meds there, then I missed setting up and didn't take any. Start over. Next morning, there should only be the AM doses in the cup. Make sure to take them and that both cups are empty before afternoon setup for evening and next morning.
I have a proxy for this system for travel, but in the case of travel, I pre-count meds into small ziplock pill bags prior to leaving home for the trip. I pack enough for the trip and a couple of extra days. Any meds whose dosage could vary during the trip get packed at "standard" dosage, with extra meds packed in bulk. Each afternoon I bring out two baggies. By bedtime, there should be one empty and one left for AM. After AM, should be none out until meds are set up for new day.
Sounds complicated, but it is like a factory kanban system. When the containers are empty, get new ones or refill them. Can see whether meds have been taken or not. Works for me.