30-Pack Kalencom Potette Plus Potty Seat Liners Classic in Camo Packaging

I have had one of these for quite awhile. I always recommend these. But mostly this specific brand. I like that the plastic bag goes over the seat it self, almost like a seat protector...Well it is a seat protector.
There are times when there are no public restrooms near by such as long road trips or camping. Or maybe the public restrooms are disgustingly dirty. I find that sometimes it's just easier to let then little one use the potty seat in the back seat floor board or in the trunk of the car, but make sure you have a blanket or towel to add privacy(or not if you dont care). Another good reason is maybe you have more then one child and one is sleeping, now you can allow your child to use the toilet without having to wake the other child. There are a ton of reasons why having one on hand in the car is great. There was one time we stopped at a view point and the mom in the car next to us walked their kid over to the only tree around and was about to have her kid squat to pee. I let them borrow our potty seat so the poor girl doesn't soil herself.
We dont buy the plastic bags that are made for this seat. We buy some simple cheap plastic bags from walmart and we've never had a leak. And in some cases we just double bag it. We also used whatever left over diapers we had as the inner liner to absorb the liquid. And once we used them up, I bought either a small pack of size 3 or size 4 diapers which is still cheap but absorbs a decent amount for newly potty trained kids.
As I mentioned earlier we use trash bags from Walmart and have never experienced a leak in the many, many times we've used them.
We buy the Color Scents twist tie 4 gallon trash bag 70 count for $4.
I assume any 4 gallon trash bag will work but we've had good luck with these ones and they are cheap.
Hope that helps.

Edit: forgot to mention, I've never used this as a toilet seat cover for public toilets. I bought this with every intention of using it as a portable toilet for the car when traveling. so I can't say how well it works for that purpose. but as a portable toilet they are great.

I sold my son on this by getting the red and blue one, putting Optimus Prime stickers on it sealed over with packing tape and called it the transformer potty. I'd put the sides out as wings and fly it around 😁

We've actually used these extensively when traveling with toddlers. Never had any problems.