Magento

I have a product that I want to be configurable where if the customer chooses they can add additional features to the base product if they wish.

Each additional feature would have its own set price. How can I set this up properly?

you are saying that.."customer can add additional gift when they are buying? “
If you want like this then add custom field with checkbox in configurable product and set price for that.so if customer will select that gift then they will get charged for that,,

No, if a customer wants to purchase a computer for example but instead of having the default hard drive they want a 1TB for example then they can add one for an additional $50.00 is this possible in Magento?

Bundle products, but they are difficult to manage.