does anybody know if it would be OK to buy shampoo/conditioner etc once through check in
Hi Tet ... no, not immediately after check-in while you are still landside, but after security when you are then airside. Toiletries purchased airside are not affected by security restrictions, and as long as you comply with the maximum weight and dimensions of your single piece of hand luggage, you will not upset Ryanair either. However, any liquids purchased after check-in but before security could be confiscated if they do not comply with current hand luggage restrictions.
David