There is a total of 8 Strandloper series geocaches on the section between Haga Haga (start of day 3) and Gonubie (end of trail). Each of them contains a hint (in the lid as well as on the logsheet) for you to collect. The hints (Strandloper Strandloper Hiking Trail Series #10 to #17) will help you find the "Strandloper Final Bonus" mystery cache near Gonubie.
You are looking for a regular lock-and-lock container.
More information about the trail can found below and on their website http://www.strandlopertrails.org.za/, from which the following excerpt is taken:
"The Strandloper Trail has been described as "the one trail where you can savour the feeling of solitude on an unspoilt beach and down a bar lunch in a cosy pub barely an hour later". The trail is almost 57 km in total and takes 4 days to complete. [NB: It can be done on two week-ends, if you suggest this to the Trail Manager.] It is clearly marked with little painted white on green boot prints and can be walked throughout the year. The best weather is between January and May which have warm windless days.
The Trail Manager will issue you with a tide table to assist you in planning your river crossings at the Quko, Kwenxura, Kwelegha and Gonubie Rivers. [...]
There are braai places, water and ablution facilities at all overnight sites. [...]
Day 3 : Haga Haga to Beacon Valley (23kms)
Today's walk covers 8 kilometres of rocky ledges with intermittent shingle beaches and then 15 kilometres of beach backed by sand dunes –you will walk past four beautiful estuaries, all of which may or may not be open to the sea. High dunes are the Strandloper middens, indicating the presence of hunter gatherers (Khoi or Gonaqua) who visited the coast to harvest mussels and other shellfish over 400 years ago. Other highlights include bird watching sites, fishing spots and swimming beaches.