I started cross country skiing last winter and am looking forward to getting my own gear this year. Question is how do you stay hydrated on longer ski days? I've seen people with backpacks but I'd prefer not have a pack on.
This depends on where you plan to ski. If you focus on XC resort or park skiing, I'd recommend what @Jiidmbo991 did. If you plan to venture off-trail into backcountry, I think that backpack is a must, as you need to carry a few more things than a bottle of water, so camelback can be handy.
I agree with Dmitry. Unless you confine your skiing to resort areas, emergency supplies are a must. Look up "ten essentials" and adapt to your situation. Things happen, equipment breaks, people get hurt or off trail or otherwise have problems. And as for water, be sure the container is well insulated and, if outside a resort, it is a good idea for someone in the group to carry a stove, fuel, and pan so you can melt ice or snow.