The useful things I got from startups and/or conferences over 20 years:

- light backpack (got it in 2003 at a conference and loved it so much that I tried to find out where they sourced it from when it finally broke after years of intensive use);

- mugs

- USB sticks (can't have enough as they tend to vanish)

- (unobtrusive) t-shirts

The useless swag (which I often remove from swag backs while still at the event):

- (obnoxious) t-shirts (too attention-seeking or the ones with the wrong logos...)

- most electronics

- most things made of plastic

- paper adware that doesn't really say anything except for logo and buzzwords

Good choices for swag are paper notebooks and pens, but the quality of the swag items will be associated with your brand, remember (it is true the quality has gone down in recent year, and also the spend per vendor)!

I encourage you all to speak out and give generous feedback about the swag offered to you, especially regarding utility, quality and ecological footprint.