Every Roman soldier carried a cloak which he used for sleeping and in addition each 8 man "squad" was alloted a tent which, was carried upon a mule.

It should be noted, individual legionaries would've carried the equipment they needed to be comfortable, without sacrificing combat efficiency. Thus it's possibly that in extremely hot weather with no chance of rain, the squad may decide not to pack their tent. Or if they believed food supplies would be plentiful along the march route they might decide to carry less food/water.

The point is that small unit leaders would plan accordingly and tell their legionaires what gear was to be carried and how it was to be arranged. In addition the small unit leaders probably left room for interpration, and allowed individual legionaires to make their own decisions so long as it fit with the overall plan.