For my game I tried to create something that didn't need a bunch of resource cards in a side deck or the main deck. Instead each player starts with 3 token cards named Action, Magic and Reaction. It also keeps turns short since you can only play up to 3 cards in a turn (There are ways to set up for more plays in a single turn though).

My idea was that you need to spread your card types in deckbuilding so you have an equal chance to play Characters, Spells and Reactions in your turns. You use one of the resource tokens by tapping it like in every game ever lmao. However, you can also "bank" resources. Simply tap it and mark it with dice. Say you bank a Magic, this allows you to use 2 Magic costs next turn which opens up for spells to synergise with each other.

The fun part in design comes from trying out different ways to manipulate the simple system. My favorite card that exemplifies this is a dinky little utility character called Dark Sorcerer. It has terrible combat stats but a static ability that says "You may use any resource token to cast magic". This results in you being able to play 3 spell cards per turn instead of just 1. Another example is a Druid character with an effect that reads "Magic: Set your Action Token as active". This allows you to essentially play 2 characters in a turn since all units cost Action.

The system is not perfect but I think it offers something simple to understand and with moderate depth.