When you kill the foes, they would drop their currently equipped weapons and shields on the ground.
But their reanimated corpses are not intelligent enough to take the items back, so I help them with this regards:
Whenever I kill the foes that I want to reanimate later, I open their inventory and take their weapon and shield and then give them back again, and they will equip them when reanimated.
I might even carry more powerful weapons around just to place in the fallen foes' inventory before reanimating, so whenever I Find a spare powerful weapon in a dungeon raid, I take it along and give it to my reanimated minions to make them more effective, and then take it again from their ashes to give it to another victim, and so on...