We do have this feature on some one-click applications (where a swap file is automatically created on smaller droplets) and some distributions like FreeBSD include a swap partition by default. You can add a swap file at creation by using the following script in user-data on the create page:

#!/bin/bash
 sudo fallocate -l 1G /swapfile;
 chmod 600 /swapfile;
 mkswap /swapfile;
 swapon /swapfile;
echo "/swapfile   none    swap    sw    0   0" >> /etc/fstab;

This will create a 1GB swap file as soon as your droplet boots for the first time and add it to your fstab to be automatically used on each subsequent boot.

If you are creating a droplet using the digitalocean docker-machine driver, put this unit in your cloud-config file (the one you provide to the --digitalocean-userdata parameter)

  units:
    - name: runcmd.service
      command: start
      content: |
        [Unit]
        Description=Enable swap

        [Service]
        Type=oneshot
        ExecStart=/bin/sh -c "\
          sudo fallocate -l 4G /swapfile && \
          sudo chmod 600 /swapfile && \
          sudo mkswap /swapfile && \
          sudo swapon /swapfile && \
          sudo echo "/swapfile   none    swap    sw    0   0" | sudo tee --append /etc/fstab"