I have a Hori FS3 and it is very light. It moves around on my lap and on a table and it frustrates me. I feel that these little movements are messing up my game a little bit.
What is a good way to add weight to a fight stick?
first, check the rubber feet to see if they are still grippy. If not, then replace those.
If you want, you could pop open the bottom of your stick and just glue (epoxy would be better) some weights onto the bottom. I saw one guy who built a ghetto stick out of tupperware and just taped a barbell weight on the bottom of it.
put a bunch of pennies in a zip lock and tape it to your stick? lol
Water is heavy. Fill your stick with water. 
Adhesive segmented lead weights sound like the best idea.
Fill it with mineral oil and waterproof the case. Problem solved + your stick will…cool…itself?
On a more serious note those adhesive lead weights (like the ones used to balance car wheels) sounds like a cool idea. Are they expensive?
nah, around $10 for like 6 oz ones
Nice necro.
I used tire weights in one of my sticks and it worked great. Tire weights are the little metal squares that they use to balance your tires. You can get a bunch on a sticky strip from an auto parts store.
Yup. Adhesive weight segments:
Put a bunch of them inside your stick.
I’ve found old door hinges work well too if you have any lying around, they’re pretty flat too