Fdroid is wonderful but a few crucial apps missing, therefore impossible to make it a 100 percent replacement

[easyKL]

@ervindine

an app that you can use to purchase flight tickets, (…) to make a booking of hotels and stuff.

Those web services always allow you to use their site.
In fact, we should start relying on our browser to get flight tickets or accommodation booking.
Try a sandbox like WebApps. It might break some websites, but still very useful.