As a measure of appreciation it is often the case that in research participants are gifted with some small token for their time in participating in research. As PhD students our funds are limited but could anyone tell me if they have used any tokens to thank their participants or used any incentives to have participants engage in the first place.

There are often ethical reasons not to offer incentives for taking part...

I don't offer my interviewees anything at all, but they do get the transcript of their interview, which is often about 20,000 words long and all about them, and I think it's a nice thing to have.

I know a research student who has given out tea bags as a “thank you” for participation.

You could give them your research results instead of transcripts. In any case, it is important to assure them that everything they say will be treated in strict confidence

I was critiqued by a grant committee for not including 'thank you' gifts in my proposal, so when I reapplied I included them in the budget, however my advisor thought that requirement was ridiculous - plus unafforadable - so unless I get the grant, my thank you gift will be in the form of coming back to the organizations I recruited from and doing a talk on my findings.