Here's a list of different things you can express in union types in TypeScript. This list is particularly useful to application developers:

- HTTP request methods: 'GET' | 'POST' | 'PUT' | 'DELETE'
- CSS length units: 'em' | 'ex' | 'ch' | 'rem' | 'vw' | 'vh' | 'vmin' | 'vmax' | 'px' | 'cm' | 'mm' | 'in' | 'pt' | 'pc'
- Boolean values and null: boolean | null | undefined
- User roles: 'admin' | 'editor' | 'contributor' | 'subscriber'
- Days of the week: 'Monday' | 'Tuesday' | 'Wednesday' | 'Thursday' | 'Friday' | 'Saturday' | 'Sunday'
- Payment methods: 'credit_card' | 'debit_card' | 'paypal' | 'bank_transfer'
- HTTP response status codes: 200 | 201 | 400 | 401 | 403 | 404 | 500
- Navigational directions: 'north' | 'south' | 'east' | 'west'
- Social media buttons/icons: 'facebook' | 'twitter' | 'instagram' | 'pinterest' | 'linkedin'
- Meal types: 'breakfast' | 'lunch' | 'dinner' | 'snack'
- Weather conditions: 'sunny' | 'cloudy' | 'rainy' | 'windy' | 'stormy' | 'snowy'
- Product sizes: 'small' | 'medium' | 'large' | 'xl'
- Programming languages: 'JavaScript' | 'Python' | 'Java' | 'C#' | 'PHP' | 'TypeScript' | 'Swift' | 'Kotlin' | 'Ruby' | 'Go'
- Currency symbols: 'USD' | 'EUR' | 'GBP' | 'JPY' | 'AUD' | 'CAD' | 'CHF' | 'CNY' | 'HKD' | 'SGD'
- Marital status: 'single' | 'married' | 'divorced' | 'widowed'
- File formats: 'pdf' | 'doc' | 'xls' | 'ppt' | 'zip' | 'mp3' | 'jpeg' | 'png'
- Music genres: 'rock' | 'pop' | 'hip_hop' | 'jazz' | 'classical' | 'country' | 'blues' | 'electronic'
- Time zones: 'GMT' | 'EST' | 'CST' | 'PST' | 'JST' | 'AEST' | 'CET' | 'EET' | 'IST'
