Flying Ryanair - car seat & pram

If your car seat and base fits in one box then that will be ok. As theyre quite strict about the '2 items'. No recommendations for a bag but I think a box would be the best idea as you can pack it more.
In my experience airlines, especially ones like Ryanair, take the buggy off you to be stored in the hold, even if the buggy is within the dimensions to be taken on board. If you have paid for Priority you might be guaranteed to take this on but best to check with Ryanair.

Also just a note, if your using a car abroad it might not have isofix so the base would be pointless. I'd just take the car seat and belt it in, saves taking more items.
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What Cybex is it? The cloud t/z you can seatbelt into a car

Yeah we took our cybex car seat abroad without the base as you can use the seatbelts of a car to instead

With Ryanair your buggy will likely be checked in unless you pay for a bag in the cabin, even though buggies travel for free. You can keep it til the end when you board the plane though.
As other ladies have said, you don't always need the base! Practice belting it in at home and if you're happy with that then leave the isofix behind. Isofix is for convenience not necessarily because it's safer, if that's a worry for you.