Start with this Du'a
Entering the market
لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ، لَهُ الْمُلْكُ، وَلَهُ الْحَمْدُ، يُحْيِي وَيُمِيتُ، وَهُوَ حَيٌّ لاِ يَمُوتُ، بِيَدِهِ الْخَيْرُ، وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ
La ilaha illa-llahu wahdahu la sharika lah, lahul-mulku wa lahul-hamd, yuhyi wa yumit, wa huwa hayyun la yamut, bi-yadihil-khayr, wa huwa 'ala kulli shay'in qadir.
“There is no god but Allah, alone, without partner. His is the dominion and His is the praise. He gives life and causes death, and He is Ever-Living and does not die. In His hand is all good, and He has power over all things.”
Jami at-Tirmidhi 3428, Sunan Ibn Majah 2235 (hasan per al-Albani; weak per Ibn Hajar, al-Arna'ut and others)
The words are a sound declaration of Allah's oneness. The narration promising great reward for saying them on entering a market was graded hasan by al-Albani and weak by Ibn Hajar, Shu'ayb al-Arna'ut and others, so remember Allah (SWT) in the market without relying on the specific reward.