With a cellphone and a Pm3 Easy you get around 80% of the capability you’d ever reasonably need. Be aware that the RDV4 version is an option, though it provides only a few small benefits when compared to the Easy (namely modularity, you can add wireless/battery modules and whatnot, though at a much higher price. The Easy is the way to go for most people.
To get that number closer to 100% you’ll likely want:
-Some Field Repeaters (RSP)
-Field Detectors (CoinStyle/xFD)
and most importantly
-A card pack or some other test cards/tags.
Midwest Gadgets has some other neat stuff you may be interested in as well, but I’ve gotten along fine with the above.
I mentioned cell phone above, the apps TagInfo, TagWriter and MCT (the latter of which is Android exclusive iirc) will do a lot.