You can make a select field required with the following:

<select class="form-control" id="basicQuoteSelectPackage" name="basicQuoteSelectPackage" required>
  <option value="">Select package</option>
  <option value="Basic: logo design">Basic</option>
  <option value="Standard: branding pack">Standard</option>
  <option value="Pro: logo &amp; branding pack">Pro</option>
  <option value="Pro: logo &amp; branding pack">E-commerce</option>
  </select>

The important thing to note is the required attribute in the opening select tag. It should also be noted that the default option "Select package" should have a value = "". The check as to whether or not something has been selected is based on the value attribute, so if this is blank, then this means that nothing was selected, hence triggering the validation.