I've been working on Pocket City 2 in Unity for several months now and have been really impressed with what you can find in the asset store. Here is a list of some of my favorite tools. I have tried many assets and these are the ones I can't live without.
I've tried a few mesh combiner scripts, and I stuck with this one because it is the easiest to use. Simply select, right click, and combine! Personally I like to keep a separate uncombined prefab as a backup in case I need to change anything, but I instantiate the combined prefab during runtime.
Mantis LOD Editor
Out of all the polygon reduction tools I've tried, and this one is the easiest to use. Simply add the component and drag the slider to reduce the count. Save the mesh and you've got your new LOD mesh. Very important for my city building game where many objects are on screen at once.
Asset Hunter Pro
This tool shows you which assets you aren't using in your project and lets you delete them easily. Very useful for someone like me who downloads a lot of third party assets, but then forgets which ones I am actually using! This helps me cut down on my repo size dramatically.
You need to be able to save your game reliably and simply. This tool is great for that. Tons of features and easy to use.
Mobile touch camera
Essential if you are building a mobile top down game and need to move the camera around the world. You could code it yourself, but this works great and saves time!
I use this just for the ability to make UI containers with rounded corners, and it's perfect for that.
This tool lets you create animations for your rigged character directly in Unity. It always takes me a couple minutes to remember how to use it since I only make animations once in a while, but it is very handy and works great. I've used it to make an eating animation for NPCs, for example.
I also wanted to mention some effects that I really like. These can be applied to a variety of games.
I mostly use this for night mode in Pocket City 2, and it works great. Looks good and performant.
Screen Transitions Pro
If you want a nice cartoony way to transition between camera shots or scenes, this effect works great.
This one is awesome. It lets you surround your objects with a glow, very important for games with selectable or interactable items. As a shader noob, I expected to struggle to get this to work, as has been my experience with most shader-related assets. Not the case at all! It was super easy. Add the script to a GameObject and everything, including children, get a glow around it. What sorcery is this? 9000/5
A couple honorable mentions. I don't use these everyday but they may come in handy.
Handy tool for scripting without relying on the built-in animation state machine. Useful if your animation logic is simple and you want to avoid the extra layer of managing the state machine.
This tool extends inspection capabilities far beyond Unity's defaults. I ended up not needing it much though, but I feel good knowing I have it in my pocket in case I need to do some in-depth debugging in the future.
A small handy tool to let you resize images inside Unity with a couple clicks. Handy for shrinking textures down quickly. Bumped this down to a runner-up because it doesn't seem to automatically change the output file type (it uses the previous saved type be default, so I might resize a PNG and it might save as TGA unless I remember to change the setting).
That's all for now!
I hope you enjoyed the list! As a solo dev, it's essential I have a variety of tools that cover all aspects of the game development experience. I hope one of these tools might make your Unity journey a little easier too!