lights for Thomas

AA Alkaline batteries have roughly 2 amp hours of capacity.  If you figure that strip is going to draw 60ma (three segments @ 20ma/ea), you'll get around 30 hours of use from a set of AA batteries.

For the second car, I'd use a voltage doubler and a constant current regulator.  Here's one for the same three segments at full intensity.

Did you think of using a Lionel ground strap and collector roller? Then supply track power to GRJ's constant current driver for the LED strip.

Since the floor is plastic, it's should act like an insulator for mounting. ~$6 x 2 + shipping. or hit your parts bin if you have one.

Here is a part # for the ground strap.

Here's Thomas' double collector roller

Good idea with the rollers, and there are many other styles that you could also use that are more compact if that helps.

After putting pickups on that car, I'd also add some weight to keep it on the tracks.

Thanks for all the input. I think I'll go with batteries. When she comes over to play trains with grandpa it's never over a hour or so , 25 to 30 hours per set will last a long time, plus I have have all the parts on hand save for one more battery box.

Again thanks for the help, you guys are the best.

Greg