What you need is a bag system.
1. You can create a extra unit (dummy) which carrys some items for hero for example and then switch items between hero and bag-unit.
2. You do like "pages" so hero can switch between inventory 1 and inventory 2 for example. (based on ability for example, so if hero uses Bag-ability you store all items in variable and drop them , then you give all items from inventroy 2 to hero)
3. Custom inventory system. Creating your own can take a while and needs much knowledge. You can look in our spell section, there are some very cool inventroy systems already.