there is a [slightly] deeper meaning,
by using the word 'fruit' instead of 'lemon'
Felix is conveying that he thinks the lemon is an excessive flamboyant element,
and by inference that Bond is also excessive and flamboyant.
Felix on the other hand, is no-nonsense and straight forward, he orders a simple drink, he doesn't even bother choosing one, he's saying to the bartender, your pouring alcohol, pour me one, in simple phrases:
My friend, bring me one as well, keep the fruit.
However i'm not sure 'keep the x' is that common as a phrase, at least not that I've heard, except in 'keep the change'