What treats to give chickens?

What treats to give chickens? I expect it all comes down to taste (yes, chickens all have their own personalities and preferences just like us really) but you might be interested to know what treats mine actually like. First, apart from the commercial feed made available in their coop thoughout the day, my chicken are free range so they eat all sorts of creatures and bugs that I have no control over.
They also have three other sources of food that I do have control over:
1- The bird feeder. The small wild birds that come to our bird feeder flick through the seeds in the dispenser to eat only their favourite ones. The unwanted seeds that fall on the floor attract a lot of attention from ground-feeding birds such as black birds, dunnocks and pheasants but also from wild rabbits and probably small rodents too. My hens love them too but they get even more excited when we give them a handful of seeds straight from the bag as they get to eat ALL the seeds not just the unwanted ones!
2- Treats from the kitchen. I try to feed them lots of different types of fruit and vegetable and I quickly learn which ones are their favourites. So far, here is what I know:
They go mad over: bananas, melon, tomato seeds, kiwis
They eat - apples
They don't like- most vegetables such as carrot peels, green beans and peas, onions, leeks, peppers, etc. I know! Fussy chickens!!
3- Treats from the garden. The best way for me to bond with my hens is to do gardening. At least, I feel like I am being efficient while spending time with them! I have a lot of nettles to pull so I will be kept busy for a long time.
They go mad over: earthworms (although Willow does not like them anymore), winged ants, small orange caterpillars, millipedes, small frogs (only Holly eats them though! She pecks the top of their heads a few times to kill them and then, swallows them whole, even when 3cm long!), small moths, these orange/brown "cocoon things", black beetles, flies and maggots (*), snails (you have to crush them first so they can get at them).
They eat - small slugs
 They don't like- ordinary ants, medium and large slugs, bees, wasps.

Yesterday, I found that chickens cannot eat salamanders (it  might be a newt, not sure but this is what it looks like:

Holly became really excited when she saw that creature hidden under the earth and started to peck at it to eat it. After a few seconds, she looked like she was in a lot of discomfort. She kept opening her beak and shaking her head. She then became very subdued and quiet and sat down for a long time, like she was sulking. The creature must have secreted something that gave her a really bad taste in her mouth. But, she was alright at the end because I found a tiny frog on the ground and gave it to her and she gobbled it up.

(*) - flies and maggots did not strictly come from my garden. The flies were caught indoors, slapped against a window with a magazine. As for the maggots, I found my chickens once standing next to our wheely bin only to realise that there were maggots inside. The hens were merely waiting for the maggots to wriggle their way out through the lid and onto the floor.