Maths, Further maths and any other solid subject.
maths, further maths and physics is a popular combination but the only two you really need are maths and fm. what subjects do you like? econ and chemistry are also good subjects to consider but again not essential at all.
Something maths based?
IDK but hey
Maths and Further Maths as definites. Other subjects such as Physics, Computer Science and Chemistry would be expected, but any academic subject even if it's not a science would be good if you feel you could do well at it.
Although if you are doing Further Maths I'd strongly consider 4, as I know for Cambridge sometimes doesn't count your Maths grade if you took it in first year and you are also taking Further Maths, however it may be different at other unis, and may be changing now that all subjects are going to be linear. But that said Maths and Further Maths as a combination are often thought as less than 2 A Levels worth of work, and from experience I'd be inclined to agree.