I use mostly gatorade and juice bottles. They are like the soda bottles, but have a bigger opening, which makes pouring easier. The larger cap is also handy to write on with a crayon or sharpie as to the contents, such as "film fixer". If the bottle is mostly full, you can squeeze it a little to reduce the capacity of the bottle so it's full. (soft drink bottles works equally well in this regard). I let them sit overnight with water in them for a while to dissolve any odor prior to use.
If you re-use a food bottle, label the contents on the cap, remove the beverage label so it is not mistaken as beverage, store it locked in the darkroom, not a living space, etc.. Standard safety for liquid chemicals regardless of the container.
Dayquil/Nyquil or one of their equivalents also come with a nice plastic graduated cup marked off 5,7.5,10,15,20 ml. This is handy for measuring concentrates.