'hashtag' has become part of modern speech thanks to twitter - it's a label preceded by a # (or hash) that's used as a way to categorise a tweet’s topic(s), which then makes it easier for people to search for other tweets about those topics. (It has since been used in other social media outlets).
for example, #StackOverflow hashtag the returns all tweets tagged with this hashtag.
Although it's a social media tag, due to its popular usage in social media, it has followed that unfortunate trend of becoming a part of spoken English, particularly in 'teen-speak', similar to when people used to actually say 'LOL' when speaking due to its usage in online forums.
An example of hashtag would be:
"I nearly got into a car crash! Hashtag YOLO."
The speaker is 'tagging' his or her sentence with 'You Only Live Once'
In your example:
I kind of have everything I've ever wanted. Hashtag blessed, you know.”
...the speaker is 'tagging' his previous sentence with #blessed - in other words, he's saying that he is blessed, or experiencing good fortune in life.