Tuner?
.
Delay is a great effect but not absolutely necessary.
Then definitely a second dirt pedal...That isn't an effect
I already have one but I don't count it
Reverb....that's a no brainier.
Delay is a great effect but not absolutely necessary.
Fuzz, personally I'm not a fan but beyond that I feel that there is really very little use for one.(at least for me).
And again phaser is cool, I have one on my board but I use it very little.
Reverb is really the only universally used effect, if we are choosing from the 4 choices you gave us.