Start a new game. Use the starting given money to upgrade your weapons or buy new ones. Continue the game until the reaching the cinematic with the moral choice. Select the moral choice, then return to the main menu during the cinematic with the explosions. Select Campaign mode then choose the one that was just played. Select "New". You will have all the previously bought weapons, upgrades and money from the previous mission. However you can upgrade your weapons again. Repeat the procedure to fully upgrade or purchase all the starting weapons.