I put the water line in the deepest (~30") using 3/4" PVC but not deep enough to have water service in the garage during a super cold winter. I simply blow it out with compressed air every fall.
For gas, use polyethylene pipe for direct burial - just make sure that it is protected in the trench and when you backfill - no sharp stones. I used clean topsoil to lay a bed in the trench and then as a cover.
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Next up was the PVC conduit for electric service. 100A single phase was the plan and while you could use 1-1/4" conduit, I used 1-1/2" to make pulling easier.
I also ran an 1-1/4" PVC conduit and used that as a pulling chase for 1/2" nylon air brake tubing in case I ever wanted to supply compressed air to the house from the garage - or compressed air to the garage from the compressor in the basement.
Then a 1-1/4" PVC conduit for coaxial cable. At the time, DirecTV required 4 runs of RG-6 for the sat antenna and the garage had a an unobstructed shot at the sky where the satellite hangs out. I've since pulled out two of the coax runs (using one as a line to pull cat-6 for a new switch and WAP and reclaiming the other since it was high quality quad shield coax with a solid copper center lead). There is also a 4 conductor phone wire in that conduit - no longer used since the cell phone has replaced the hard-wired phone - or at least in the garage.
I also ran a 3/4 PVC conduit for the runners between the three way switches so outdoor garage lights could be turned on from the house and the back door light from the garage. This was a code requirement.
A second 3/4 PVC run was put in for a single 20 amp circuit from the house panel to the garage. This way I would have access to limited power if for any reason I decided to kill power to the 100 amp sub panel in the garage. I'll admit, this one was over-kill, but...
So total of :
one - 1" direct burial gas polypipe -
one - 3/4" direct burial PVC for water (no sink or urinal, but for car washing)
one - 1-1/2" PVC conduit for main power
one - 1-1/4" PVC run to contain air tubing
one - 1-1/4"" pvc conduit for communications
one - 3/4" PVC for lighting switch runs
one - 3/4" PVC for aux power
Since the distance was ~50' the extra runs didn't matter that much in terms of cost. If the distance were greater, I would have been more frugal.
Everything was in one trench, but at the time the local building inspector was a good friend and he knew that my work had integrity so he was never hung up on some of the minor bits of code requirements.
