I think the guideline should be that if you're not willing to spend enough to give away a durable good that people would actually use (e.g. a good quality t-shirt), we should normalize giving away useful, common _consumable_ goods. This can avoid increasing waste if it just replaces/delays consumption the recipient was already going to do anyway. It's shorter-lived, so they don't act as a walking ad for you (but no one was gonna wear that bandana anyway) but this way you might create some positive sentiment.

E.g. branded small sanitizer bottles, sunscreen bottles (X Corp cares about your health and well-being!), snacks (we're all occasionally hangry at conferences right?), etc.