subtlearts
Basically no matter what your main monitoring rig is, it's very important to cross-reference to a variety of systems and environments - studio monitors and headphones, quality earbuds, crappy earbuds, consumer computer speakers, laptop speakers, home stereo rigs, car stereos, phones and tablets, bluetooth speakers... obviously it makes no sense to do this with every mix decision, but as you get close to something you want to get behind, that should start. There are ways to fake it - plugins that mimic different speaker response and so on - but it's really no substitute for the real thing... and of course, the bonus is that as you do this you start to learn how your main rig translates to other systems, and you get better at predicting and accounting for that, and your mixes get faster and better. Well, that's the theory anyway!
I like to use things like Toneboosters TB Isone for a quick comparison what things '
may' be like on different systems etc, but like you said, not really a substitute for the real thing, but quick and easy and convenient.