This is one of the loveliest cycle rides in the country. It begins by travelling through bush and valley views and ends in a coast road that offers gorgeous sea views and seal colonies. It is one of the few places in the world where you can see stunning summer seascapes and snow peaked mountains all in one vista.
Picton to Blenheim (28k)
If you head to Blenheim, you will travel down the main road south, (unless you take the Port Underwood road which is empty of traffic but winds up and down and in and out of a number of small, picturesque bays for fifty odd kilometres, pretty, but no shops and a single backpackers at Oyster Bay), Blenheim is only thirty odd kilometres from Picton by main road, but I recommend continuing on to Renwick, about 10Km west of Blenheim. It's a great spot in the middle of the scenic wine growing area and has access to a wonderful eatery called The Mudhouse Café.
There is an English style pub handy which brews its own beers... nice. Don't attempt to cycle up the Wairau valley to St Arnaud (90k, no shops) to the west coast unless you have a strong south easterly behind you. Generally the wind blows down the valley from the North West and it is very slightly uphill. A good option only for those who love a challenge.
Blenheim to Kaikoura (≈125k)
The trip to Kaikoura can be completed in a day from Blenheim, but this is often a bit of a stretch for those who like meandering. A good stopover is Pedaller's Rest (a few kilometres past Ward then 1.5k up Ure River Road off SH 1). Get your main groceries in Ward. Pedaller's Rest is a lovely place and will provide a few basic foodstuffs, but there is no general store close by.
Take a moment to have a break at The Store in Kekerengu (approx. 24k from Ward). The Store has great food and very good coffee and a clear and stunning view over the Pacific. Ask locally and you may be allowed to camp among the pine trees to the north and the township close to the sea. The beach is notable for its long foreshore of flat, circular sea stones in grey, black and white.
Be wary of seals! They are easy to photograph and frequently appear to be posing for you. But in late December and January they come ashore to breed and the Hooker Sea Lion is particularly unpleasant if approached lightly.