This page tells you how to save and load game data / your variables from items, actors, anything...

Save/Load Variables

Just check this box in your blueprint.

Save/Load Custom Actors

Shoutout to CorporalWill123 for solution. This applies for all actor blueprints using just plain Actor parent: This is more problematic, because just checking SaveGame checkbox is not enough there. You have to also check bSaveGameRelevant, but there's no such checkbox/option that can be enabled through UE. You have to do it through UAssetGUI and even worse is doing it again every time you make changes in your actor and replace cooked .uasset file. The best you can do is, make most of the changes in your actor and and then just pay attention to not accidentaly overwrite it.

How to enable bSaveGameRelevant using UAssetGUI:

• Open your cooked actor through UAssetGUI and head to Export Data section.
• Find Default__ ... _C and open it
• In the list, add following: bSaveGameRelevant, BoolProperty, true, 0, False (Name, Type, Value, ArrayIndex, Is Zero)
• Save asset and you're done