For whatever reason, many moms worry about the state of their children’s underwear and what others (particularly EMTs and ER nurses) will think if of those ratty undies. With all due respect to the moms of the world, those are just the kinds of panties and bras I encourage you to pack for your next big trip. When you have finished wearing the undergarments, just toss them in the trash. It’s where they should have been in the first place. Now you have an incentive (more luggage space) to throw them away.
I’ve applied the same philosophy to other garments as well. I often pack those things that have been worn frequently and are now a little too worn/faded/shapeless/snagged… to donate. Some of my favorite pieces have been pulled out for a grand final wearing before they end up in the hotel’s trash bin. It’s a great tactic for freeing up space in the suitcase and getting rid of clothes that you’ve worn too much to donate.
Sugar, come sit a spell. 
I love this idea!!
This is one of mine: If I’m running low on a certain personal product (face lotion, makeup item, etc.), I am more likely to take it with me on a trip – with a quick look-see that I think I’ll have enough for the entirety of my stay. This way I can discard it while I’m traveling and have that much room in my DOP kit.
Note: if the hotel doesn’t have a recycle bin in my room, I ask if they do recycle and if not, then the container comes home with me. I’d rather ensure it be disposed of properly, than not.