There is no issue while keeping other options open for yourself.Because not every time luck plays well. In fact, if you can have a look on other examination and options you always feel motivated.

But according to me, having focus on one thing is better than choosing to give other exams simultaneously. Still if you have asked, I would recommend to prepare for banking or railways.

The very advantage of opting for railways is that its overall syllabus is same as that of SSC CGL.So you go for two by preparing for one. Seems easy, right?

You need to know that reasoning portion of Banking is of higher level then SSC CGL, so if you prepare well for reasoning of banking then you can solve reasoning of SSC CGL easily. As far as bank examination is concerned, you should have quantitative aptitude knowledge, Reasoning, English and General awareness.