As we serve our Lord Jesus we are not in this for the pursuit of material things. If an item is of no use in the pursuit, display, and/or spread of the gospel it is a superfluous.
If anyone teaches a different doctrine and does not agree with the sound  words of our Lord Jesus Christ and the teaching that accords with godliness, he is puffed up with conceit and understands nothing. He has an unhealthy craving for controversy and for quarrels about words, which produce envy, dissension, slander, evil suspicions, and constant friction among people who are depraved in mind and deprived of the truth, imagining that godliness is a means of gain. Now there is great gain in godliness with contentment, for we brought nothing into the world, and  we cannot take anything out of the world. But if we have food and clothing, with these we will be content. But those who desire to be rich fall into temptation, into a snare, into many senseless and harmful desires that plunge people into ruin and destruction. For the love of money is a root of all kinds of evils. It is through this craving that some have wandered away from the faith and pierced themselves with many pangs. (1 Timothy 6:3-10, ESV)
In this example Musashi is of course coming from a professional soldier's point of view. When he speaks of military equipment is it things needed in the pursuit of his profession, his purpose in life. We as Christians ultimately need nothing. For when Jesus sent out His disciples these were His instructions:
And he called the twelve together and gave them power and authority over all demons and to cure diseases, and he sent them out to proclaim the and to heal. And he said to them, “Take nothing for your journey, no staff, nor bag, nor bread, nor money; and do not have two tunics.  And whatever house you enter, stay there, and from there depart."(Luke 9:1-4, ESV)
Anything extra is a distraction and a hindrance in your pursuit of God and your service to Him.