How to future-proof a long cable run
Empty conduit is your best bet here. No point in guessing what (if anything) you may get, and guessing wrong. While you can leave a pull string in it, you can also just vacuum a pull string into it when the time comes (that's what is normally done to install it in the first place). If you do leave a string, don't worry about how big/strong it is:  it can be used to pull in one big/strong enough when the time comes. Do make sure it won't rot while it's waiting. And CAP THE ENDS of the empty conduit, or it may not be as empty as it should be when you need to use it.

Speaking from personal experience, assuming you don't need more than one for excessive bends/sweeps (and do use long-radius sweeps when you do need to make a bend, not the short radius stuff from home centers) you will be much happier with a pull box/hand hole/access at the halfway point.

I have hand pulled (no winch) fiber over 600 feet. It was not much fun. With correct technique (pulling on the Kevlar, not the fiber or the jacket), possible, but no fun. 330 feet/100m it should be easy (was for us) if the conduit is configured correctly (large-radius sweeps, no more than 360 degrees of bending between access points.)

Enter (and leave) the pull box with 45s, not 90s. Leave some extra cable coiled up in the pull box in case of any future need for more at either end due to damage. Before pulling cable in, see figure 8 coiling and use it so you can pull the cable in, figure 8 coil the other half, flip the coil and pull it the rest of the way - no tangles.

For political/turf (rather than electrical) reasons, it's often best to keep cable, telephone and "whatever is next" in separate conduits. It's also much less practical (or more difficult) to pull into a conduit with a cable in it - often best to remove the original cable and pull the new cable and the original cable back in together, rather than trying to pull a new cable in next to the original - but best if you can just pull the new cable in its own conduit and leave the original cable/conduit alone.

Additional suggestions - 


If using PVC conduit, choose schedule 80, and deburr (remove sharp inside edges from) the male ends of the joints.
If you can get polyethylene conduit, consider it as you can get
100 meters with no joints and it's more flexible than PVC
(effectively the same as polyethylene water pipe, with different
certifications stamped on it)
Do not neglect the locating/warning tape - whether it says buried fiber optic below or buried telephone line below does not matter nearly as much as that it is there in the top of the trench, directly over but well above the conduits.