I used to carry three approx 3 foot 2x8 boards. When I got a couple packs of the plastic blocks, I started carrying two boards.
Usually if I have to level more than two boards high, I try to see if I can park the TT somewhere else. But between the boards and blocks, I have been fine so far.
If I don't need the blocks for leveling, I can use them under the stabilizer jacks, under the front jack, under the picnic table, to level the grill, etc.
I have also found that a simple 2 foot long 2x4 seems to come in handy all the time, usually for grill or table leveling.