First of all, I want to apologize if this thread is in the wrong forum.
I couldn't figure out where it should go.
MOD: please move to proper forum if necessary.

I have a BUNCH of DVDs and BDs that came with my purchases of UHD and BDs.
Don't need or want more than one copy of a movie and would like to sell them.
I have been putting them in simple paper sleeves and setting 'em aside without ever being played or used.
What do you all do with yours?
Suggestions appreciated.

I keep them in the case where they belong. They're part of the overall package.

Ebay

What difference does that make?

Likely none to anyone but me. I'm somewhat OCD in that I keep all packaging, right down to inserts and label stickers (other than store added ones) "just because." They also don't take up any extra space in the case. Few people are interested in purchasing "white envelope" discs and those that do won't pay enough to make it worth messing with.

I hold on to them because the room my kids watch movies in doesn't have a blu-ray player, so they get to watch Lego Batman or whatever on DVD.

I like to hold on to them as backups.

And me. I even WATCH them, because they're there- but I won't be sad when they finally stop including them.

Probably no surprise, but I keep everything too. I’ll throw away the plastic wrap, after cutting off any non-store stickers, but that’s it.

And I keep the DVDs because there are still places I watch movies with only DVD players (mom’s, work, car...). And if the BD gets damaged, lent out, or lost, might as well have the DVD around.

I keep mine to use as a backup in the case as well. I found out the hard way that it is good to have them. When my old Blu Ray player died, I had the Blu Ray of Attack Of The Clones inside. Since there was no way to get the disc out, I used my DVD instead.

I offer it to friends/family. If there are no takers, it usually gets trashed, along with the case and slipcover.

I hate the idea of trashing a perfectly good DVD or BD...seems like such a waste.
OTOH,....

I just leave them in the case UNLESS

I need the hub for a store exclusive bonus disc, like the Target Avengers when the exclusive comes in an envelope. I put the bonus disc in the case with the blu-ray, and then stash the DVD in the envelope.

It's a "stacker" case, which I hate, and I take the DVD out and put it in a paper envelope.

I keep the package deal intact, it's just part of being the collector that I am. I'd also never buy movies in paper sleeves, if it doesn't come in the original case with the goodies intact, I don't want it. I go to flea markets, there is this one seller who always removes the DVDs from the BD/DVD Combos (and apparently sells them separately), if he'd left them complete I might have bought some from him, but he doesn't and I haven't.

One of my other reasons for pulling extra disks is the weight reduction.
At last counting, I have 8,000 DVDs, BDs, UHDs, and CDs.
Lugging them between houses becomes a problem when you are 62 years old...

^ I am 62 as well, my videos (currently 1138, counting TV seasons as 1) are housed in 4 big 5 & 6-shelf bookcases. My wife and I are permanently settled in our house and we have no reason to want to take anything with us when we go anywhere so they don't ever leave the house. I can understand your concern with weight if you move around a lot, that would be a consideraton with me as well, but I'd still have a hard time separating videos with my current mentality. They just wouldn't seem whole to me...

Try moving CED videodiscs- no 5-inch disc weighs anything CLOSE to those!

"Extra" dvds? No such thing. The DVD included in the blue ray packaging gets used anywhere there isn't a blue ray player, which is a lot of places. Car, portable player, kids room, sisters, grandparents, etc.

I just leave them in the case.

As others have said, they make a nice back up.

I just keep them in the case. On the off chance that I go to someone’s house who doesn’t have a Blu-ray player and wants to watch a movie or someone wants to borrow a movie I volunteer the DVD first normally. I see no reason to get rid of them and it’s not worth the effort trying to sell them.

It's funny about the weight thing...
It doesn't take many to make a moving box weigh too much to move without getting a hernia (something I have learned the hard way).

That's the thing...I don't go anywhere where a BD player isn't available.

I'll be having a garage sale this spring...maybe I'll just put them in a $1 box.

I keep and use them to make screen caps for Facebook references and cover photos.

Like others, I like to have the DVD as a back-up or to use in situations where a Blu-ray player isn't available.

I have a number of self-made combo packs. If I really like a film and it have it on both DVD and Blu-Ray, I'll put both editions in a double blu-ray case so they'll be in the same place. I especially do this when the DVD is in one of the old "snapper" cases.

Someone recommended I donate them to a Boys Club or library or a non-profit of my choosing.
That way I could write them off on my taxes.

I hope you did that before 12/31/17. Unless you can somehow still itemize more than 12000/24000.