Hi AJ, you can perhaps buy self steering (maybe an older autohelm for wheel steering) through eBay. But, new is better and new is also relatively expensive. There are however a few things you can do to keep the boat on track while you visit the foredeck.
For years I had only a hydraulic Hydrive system. They are good because they don't move once set. That's great for trade wind sailing and for short absences, such as a wander across the deck or making a cuppa below. If you tighten the friction lock on your binnacle, you can achieve the same effect with mechanical steering...just remember to back it off when you return to the cockpit.
But, and as I am sure you know, it's a big but, all this locking off is dependent on wind from a constant direction and trimmed sails. If you go forward to 'mess about with the sails' the trim will be affected and so will your subsequent direction of travel.
If you are sailing shorthanded, I imagine your lines are all led back to the cockpit. Going forward is still possible, but you need to first set the sails, lock off the wheel to balance the boat, then go forward to stretch your legs rather than to alter trim.
Island Packets are wonderful boats and maintain good direction but I fear you will need to eventually buy a self steering system so that you can sit up on the bow and thereby occupy the best spot on the boat in a three to four foot sea with wind on the beam.
Things would be immeasurably easier if you had a tiller (sheet to tiller self steering is a joy to behold) and I offer this link purely because it is interesting: Sheet-to-Tiller Self Steering
I wish I could be of more assistance. Best wishes.