Some items are GPL compatible, some are not. If that’s the type of item you’re after then it’s best to check for that type of item before purchase. Search for GPL on CodeCanyon to see.
Some items have the “100% GPL” license. The code for these can be included in projects and distributed on github as per normal GPL guidelines.
There are some more details and examples here: https://codecanyon.net/licenses/faq#small-element-stock-a
Otherwise no, your purchased item cannot be included in another product and distributed as source (without the authors permission).