I ask this literally, not rhetorically: are you saying that the Luke passage abrogates the Sermon on the Mount? All those teachings (the related ones, in any event) were in effect for the very, very short period between the time the speech was given and the night Jesus was betrayed?
A fine question. I am not saying that the Luke passage negates the Sermon on the Mount. Neither does the Sermon on the Mount negate the Luke passage. Jesus spoke to the masses, and gave them the SoM. He spoke to the apostles and told them to carry a piece. So is this contradictory? I don't feel so; rather, it is complementary.
The ideas here in Proverbs are complimentary, you need to use a bit of wisdom, a bit of prayer, and apply the appropriate one. Sermon on the Mount and Luke? Complimentary, not contradictory. Use some commons sense, give it a bit of prayer. God tell you to carry some heat going down a dark alley? Do it. He tell you to carry nothing other than a pocket New Testament? Do it.