Hey Shubhi,

With this question I found it helpful to think about the 'intent' of the words as well. The sentence gives us a clue with the last half: "it is best to conduct only essential errands, and to do so with haste." Because of this, and because of the hint "unnecessarily" in the first half, we know the word must be something that means non-hasty or non-essential walking.

The choices make this distinction difficult: all of them are associated with movement, usually walking. Because of this, we have to think about the intent of the word -- which what most closely resembles non-essential walking?

'Bop' can mean to travel energetically. This is too far from our intended blank to readily consider.
'Traipse' means to move wearily, and can also mean walking casually or needlessly. Needless is similar to non-essential -- we should come back to this one.
'Circumambulate' means to walk the circumference, or all the way around. Walking all the way around the city would certainly be needless. We can question: would one 'circumambulate' downtown for some essential errands? It doesn't quite fit, but we should remember it.
'Sidle' means to walk furtively, or secretly. Not very close to 'needlessly,' although it is used colloquially to mean 'slip over' to one building or another.
'Reconnoiter' means to travel with the purpose of making observation. Not very close.

So we're left with possible options as traipse, our most likely; circumambulate, one that fits halfway; and sidle, which only colloquially would really fit the blank. We can cross out sidle, as it's rare GRE vocab question focuses on colloquial usage. And between the last options, traipse is a better fit because it more closely matches the intent of 'needless' or unnecessary walking.

This was how I thought about the question -- I hope I didn't make things more confusing.