I use fairy lights like these too sometimes. I use a lighter weight version with a single button battery. They only weigh 13g (less than 1/2 ounce) each. They also make versions with two button batteries. I keep mine in a snack-size ziploc bag and use a couple of twist ties to connect to my ridgeline. They're more fragile than a pen light, but if you're not too rough with them, they'll last many trips. Even when they break, it's not much of a concern because they are so incredibly cheap (the example below is $9 for a 12-pack).
There are a lot of options out there. Here's just one example:
https://www.amazon.com/Fibevon-Water...1zcF9idGY&th=1
(Side tip ... if you need 2032 button batteries, it's cheaper to buy these lights and remove the batteries inside than to buy the batteries separately.)