whats the correct way of inserting label in an Ionic FAB list

If you are using ionic 4, this is for you

ion-fab-button[data-desc] {
  position: relative;
}

ion-fab-button[data-desc]::after {
  position: absolute;
  content: attr(data-desc);
  z-index: 1;
  right: 55px;
  bottom: 4px;
  background-color: var(--ion-color-dark);
  padding: 9px;
  border-radius: 15px;
  color: white;
  box-shadow: 0 3px 5px -1px rgba(0,0,0,0.2), 0 6px 10px 0 rgba(0,0,0,0.14), 0 1px 18px 0 rgba(0,0,0,0.12);
}

<ion-fab horizontal="end" vertical="bottom" slot="fixed">
    <ion-fab-button color="primary" class="">
      <ion-icon name="add"></ion-icon>
    </ion-fab-button>
    <ion-fab-list side="top">
      <ion-fab-button color="primary" routerLink="/contacts/create" routerDirection="forward" data-desc="Create Contact">
        <ion-icon name="person-add"></ion-icon>
      </ion-fab-button>
      <ion-fab-button color="primary" >
        <ion-icon name="stats"></ion-icon>
      </ion-fab-button>
      <ion-fab-button color="primary" routerLink="/reminder/create" routerDirection="forward" data-desc="Create Reminder">
        <ion-icon name="alarm"></ion-icon>
      </ion-fab-button>
    </ion-fab-list>
  </ion-fab>

I Ionic 4/5 the accepted answer (labels next to icons) doesn't work anymore. You have to use ::after pseudo css styling using a global attribute like item or data-. See the example below:

HTML:

<ion-fab vertical="bottom" horizontal="end">
    <ion-fab-button>
      <ion-icon name="add"></ion-icon>
    </ion-fab-button>
    <ion-fab-list side="top">
      <ion-fab-button (click)="do1()" data-desc="Description 1">
        <ion-icon name="contact"></ion-icon>
      </ion-fab-button>
      <ion-fab-button (click)="do2()" data-desc="Description 2">
        <ion-icon name="person-add"></ion-icon>
      </ion-fab-button>
    </ion-fab-list>
  </ion-fab>

SCSS:

ion-fab-button[data-desc] {
  position: relative;
}

ion-fab-button[data-desc]::after {
  position: absolute;
  content: attr(data-desc);
  z-index: 1;
  right: 55px;
  bottom: 4px;
  background-color: var(--ion-color-primary);
  padding: 9px;
  border-radius: 15px;
  color: white;
  box-shadow: 0 3px 5px -1px rgba(0,0,0,0.2), 0 6px 10px 0 rgba(0,0,0,0.14), 0 1px 18px 0 rgba(0,0,0,0.12);
}

Source: https://forum.ionicframework.com/t/fab-labels-in-ionic-4/139823/6

For what it's worth, I was able to accomplish what you ask with the following SCSS.

It'd be nice if this was supported directly by Ionic, but I can't find anything indicating this is built-in.

    button[ion-fab] {
        overflow: visible;
        position: relative;

        ion-label {
            position: absolute;
            top: -8px;
            right: 40px;

            color: white;
            background-color: rgba(0,0,0,0.7);
            line-height: 24px;
            padding: 4px 8px;
            border-radius: 4px;
        }
        contain: layout;
    }

ross solution is great,but in order for it to work on Ionic v2 I had to change the .fab class that comes with Ionic from contain: strict to contain: layout.

This is how the class is originally:

.fab {
    -moz-appearance: none;
    -ms-appearance: none;
    -webkit-appearance: none;
    appearance: none;
    position: relative;
    z-index: 0;
    display: block;
    overflow: hidden;
    width: 56px;
    height: 56px;
    border-radius: 50%;
    font-size: 14px;
    line-height: 56px;
    text-align: center;
    text-overflow: ellipsis;
    text-transform: none;
    white-space: nowrap;
    cursor: pointer;
    transition: background-color, opacity 100ms linear;
    background-clip: padding-box;
    -webkit-font-kerning: none;
    font-kerning: none;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    contain: strict;
}

So, add the following on your page .scss file:

.fab {
    contain: layout;
}

It will overwrite the default .fab class for the page and it will work.