I’ve bought some useless fishing gear in my time, the stuff that you only use once and then sits in the bottom of my bag or the garage for years. But recently, I’ve bought a couple of things which have been very useful:

Aquasure
This is a flexible, waterproof glue which is used for repairing waterproof clothing and equipment. However, its an excellent option for sealing braided loop onto your fly line. I only use the Roman Moser loops now as they are small, neat and have much less braiding. However, using superglue adds an element of stiffness to the end of the line and I still find the braiding gets frayed after a while.

Aquasure works really well. It gives a strong but flexible bond. Using a brush, you can also work it down the braid which fixes it in place without being stiff.

Whizz Lube
Sounds dodgy but works a treat! I’ve had a couple of line cleaners before which seemed to leave the line slightly tacky. Whizz Lube is excellent. I give the line a good wash, dry it thoroughly, then add the Whizz Lube (which has a useful applicator built in) and let it dry. Then, once dry, I run it through a dry cloth, to give it a buff, as I wind it back onto the reel. It may seem a lot of effort but it gives the line a really good sheen and helps it fly through the rod rings.