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.