walnut alternative

Small squares of apple? Chopped carrot? Banana goes particularly well with dates but I am not sure pieces would remain whole in a cake. Other alternative is just to increase the quantity of dates - perhaps add a fancy topping when it is baked?

Definitely the chocolate!

I would go for the chopped mixed peel as well. It gives a lovely flavour.

Apricots?

If the walnuts are just an added ingredient - as in they are just in the mixture rather than a necessary component there is nothing to stop you leaving them out. However, if I am making something similar and do not have all the things I need I just throw it whatever is around. E.G. raisins, chopped apricots, sunflower seeds, chopped peel, chopped dark chocolate etc etc.