What is the 'easiest' way to add canonicals or redirects manually?

For different reasons it isn’t possible to utilise a global plugin so what would be the easiest/best way to

1) add manual canonicals to blog posts

2) an alternative to the above would be to add redirects… but again manually

There are some posts that I may not want to add a canonical to or redirect hence the need to do it manually…

Thanks…