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