The inner tube floats with covers are nice dive floats and you can carry equipment in them and salvage you may pickup, trash etc. I currently am using the bob float type flag, no inner tube, just a weighted float with a flag on it. I sometimes when diving from my kayak tow it, in fact, I rarely anchor it except temporarily while I swim the anchor line and then pick it up. I use a small kayak anchor which weaighs a couple of lbs. I have towed my 14 foot inflatible with 35 horse engine also in the same manner. The kayak and the inner tube generally provide very little drag and neither does the bob float.
As to flags and boaters, there will always be idiots so be prepared. pelican Industries I think makes an aluminum device similar to what you see for extension cords. You just wrap the line over it. I use cave line or a small poly line, brightly colored--nothing super heavy is needed. In any case i would never clip the line off to me but instead just hold it. The small kayak anchor is nice because you can set it down to explore and area and then come back and pickit up. They only weigh a few pounds (1 to 1.5 lbs to as much as 3 lbs) and generally fold up and have a cloth/nylon bag.
Now I have taken to diving from our Boston Whaler leaving my wife on deck to scream and holler at the yahoos. N