Brick Filler Or Something Like It (CT3)

To fill hole before new fence is put up my neighbour, as I want to ensure it's filled with correct stuff, as I've read that if wrong stuff is used, it could cause more problems due to temperature change or if it was ever removed by a new neighbour it could damage the wall more.
Many thanks if there is a small tub of cement type stuff that can be used for walls if anyone has any spare they no longer need.
Dead line is just as soon as possible, I cannot state a date, it could be too late if I cannot get stuff fast !!