Teachers, counsellors, coaches and other people who work with kids every day get invited to many graduation parties each year, especially if they’re well liked or make a significant contribution to the community. The dilemma these folks face is whether to bring a gift to every party they attend.
In general, gifts are not mandatory and it would be unrealistic to expect teachers, school staff, coaches, etc. to bring gifts to every party they attend. In fact, most grads don’t expect gifts from these people. They’re just thrilled if their mentors take the time to come to their party.
If you’re invited to a lot of parties and can’t afford to bring a gift to each one it would be nice if you could make or buy a card and write a little congratulatory message or words of wisdom to the grad. But even that’s not necessary. Just making an appearance to the party is often “gift” enough.