Check out Unity packs with generators for vegetation, buildings, and city creation that will come in handy for your Unity project. 

Real Ivy 2 Procedural Ivy Generator

• Grab a cool plant generator for Unity from 3Dynamite. 
  Details:
• Ivy Painting system
• Procedural growth system
• High quality presets system
• Design time and Runtime support
• Normal mapping, reflections, PBR support
• Customizable leaves and branch shapes
• Place by clicking in the scene view
• Customizable growth path
• Lightmapping support
• Optimized meshes
• Friendly UI

Gaia Pro - Terrain & Scene Generator

Create terrains and scenes in Unity procedurally or manually with Gaia Pro generator.
What’s inside:

• Multi Tile Terrain Support;
• Powerful Biome Creation & Mixing System;
• Massive World Creation with Non-Destructive Editing;
• Massive World Streaming, Culling & Floating Point Fix Support;
• Vegetation shaders with location and seasonal variation, sss, cover, and snow;
• Asset shaders with location and seasonal variation, sss, world cover, and snow;
• Over 100 Photogrammetry Enhanced assets;
• Beautiful & configurable lighting system with a time of day support;
• Spawnable VFX system with birds, butterflies, falling leaves, and pollens;
• Spawnable Sound FX system with a range of sample sounds and music;
• Integrated & matched skies, lighting, fog, and post fx for beautiful visuals;
• Integrated weather system with rain and snow support;
• Beautiful & Fast Water Shader and presets system;
• First, third, flying & VR/XR character controllers;
• GPU accelerated Stamping & Spawning;
• Real time stamp & spawner previews;
• LODDed Terrain Mesh Export system;
• Layer based asset culling system;
• Builtin, URP & HDRP 7.2+ support;
• Stackable filtering system;

BuildR Procedural Building Generator

• Craft a wide variety of buildings for your city project using a generator from Jasper Stocker.
  Features:
• Generate buildings at runtime OR in the editor.
• Create endless buildings with complex explorable interiors.
• Use custom models to accentuate your buildings and give them character.
• Generate any size from small village houses to complex urban towers.
• The multithreaded parallel design takes generation off the main thread and free up your frame rate.
• Supports all Unity platforms from mobile through to AAA.
• Asset based - create buildings that can be transferred easily between projects.

Fantastic City Generator

Take a look at the city generator for your games. 

• Some details of the pack:
• Realistic cities of various sizes, with rivers, tunnels and bridges.
• Contains 237 unique buildings and several 3D Objects.
• Very easy to add third party Buildings
• Includes Vehicle Traffic System with lowpoly cars
• Resize City Manually
• Apply Mesh Combine with one click

Seamless Texture Generator

Grab a cool texture tool to add to the Unity editor.
Key features:

• Generating seamless textures from files inside the project
• Functional custom inspector window
• Clean preview for the seamless generation process
• More functions soon when a package will be developed more
• Full source code included