Extend entities with stay able to upgrade

Hello!
I have next problem. I need to write website with nopCommerce as base. I want extend nopCommerces entities with my own fields and implement custom buissnes logic. How can I do this and stay able to update nopCommerce in future?

Plugin can resolve problem with update, but I dont know how extend entities with plugin.
Please, help me in my issue.

I would use IGenericAttributeService. It allows you to extend any entity without a need to modify a database or core entity classes. Have a look at how it's already used with [Customer] entity.
P.S. IGenericAttributeService was added in version 2.60

genericattributes is very slow. how to extend entities with plugin?

ex.

public partial class ShoppingCartItem : Nop.Core.Domain.Orders.ShoppingCartItem
    {
        public bool blabla{ get; set; }
    }