Mixins I commonly use.

_mixins.scss

@mixin font-smoothing($value: on) {
  @if $value == on {
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
  }
  @else {
    -webkit-font-smoothing: subpixel-antialiased;
    -moz-osx-font-smoothing: auto;
  }
}

@function lower-bound($range) {
  @if length($range) <= 0 {
    @return 0;
  }
  @return nth($range, 1);
}

@function upper-bound($range) {
  @if length($range) < 2 {
    @return 999999999999;
  }
  @return nth($range, 2);
}

@mixin between($min, $max) {
  @media (min-width: #{$min}) and (max-width: #{$max}) { @content }
}

@mixin min($size) {
  @include mq((min-width: #{$size})) { @content }
}

@mixin max($size) {
  @include mq((max-width: #{$size})) { @content }
}

@mixin grid-row() {
  @include outer-container();
  @include pad(0 $gutter/2);
}

@mixin collapse-right() {
  padding-right: 0;
}

@mixin collapse-left() {
  padding-left: 0;
}

@mixin collapse() {
  @include collapse-left();
  @include collapse-right();
}

@mixin zero() {
  padding: 0;
  margin: 0;
}

@mixin plr($pad) {
  padding-left: $pad;
  padding-right: $pad;
}
@mixin ptb($pad) {
  padding-top: $pad;
  padding-bottom: $pad;
}

@mixin mlr($pad) {
  margin-left: $pad;
  margin-right: $pad;
}
@mixin mtb($pad) {
  margin-left: $pad;
  margin-right: $pad;
}

@mixin button($rest-color, $hover-color: $rest-color) {
  background-color: $rest-color;
  border-radius: 0;
  color: #fff;
  display: inline-block;
  font-size: 1em;
  line-height: 1;
  padding: .75em 1em;
  text-decoration: none;
  @include font-smoothing(on);
  @include transition(background-color 200ms ease);
  &:hover {
    background-color: $hover-color;
  }
}