is a Sentence Ending Particle. It has the same meaning as よ。, but it is verycasual andspoken-language .
あのさ Hey, uhh...
何もできなくてさ I wasn't able to do anything, y'know
Some people really tend to overuse this word as a filler word.
ディズニーランドに行ったんだけどさ、なんかさ、凄い込んでて I went to Disneyland, like, and it was, like, really crowded.