Travelling next year with a 4 and a 5 year old and am wondering about booster seats. I've seen some of the prices quoted by rental companies 
My take on it is that you are not required by law to have a booster seat but rather that the seat belt should fit/be positioned correctly. So will I be able to get away from rental company without them saying I have to have one - I'm sure they will imply that anyway.
I was thinking of either buying a couple of booster seats while out there - my kids are not tall enough to get away without one in my car so am assuming the same over there.
Can you use seat belt adjusters to change positioning of belt?
I've read some people that took theirs with them but would not trust them to arrive in one piece if outside luggage and am loath to give up space inside luggage as I would need them back.
My third thought was to buy a couple of cheap ones here, take in luggage and them leave them in car or in a bin at the airport. Our luggage will not be full on the way out but may be on the way back...
My last bit is has anyone taken/used Trunki Boostapak. Booster seat and backpak combined that could be used for games/food for plane and then obviously as a seat in rental. £30 - £40 depending on where you look.
Any thoughts or comments please.

My take on it is that you are not required by law to have a booster seat but rather that the seat belt should fit/be positioned correctly. So will I be able to get away from rental company without them saying I have to have one - I'm sure they will imply that anyway.
I was thinking of either buying a couple of booster seats while out there - my kids are not tall enough to get away without one in my car so am assuming the same over there.
Can you use seat belt adjusters to change positioning of belt?
I've read some people that took theirs with them but would not trust them to arrive in one piece if outside luggage and am loath to give up space inside luggage as I would need them back.
My third thought was to buy a couple of cheap ones here, take in luggage and them leave them in car or in a bin at the airport. Our luggage will not be full on the way out but may be on the way back...
My last bit is has anyone taken/used Trunki Boostapak. Booster seat and backpak combined that could be used for games/food for plane and then obviously as a seat in rental. £30 - £40 depending on where you look.
Any thoughts or comments please.