St Lucia is as safe as any other country. However you should exercise the same caution as you would at home. Pickpockets are in every country - just be careful in crowded areas.
Use of camouflage bags is illegal in Saint Lucia if you're not military personnel. If you show up at the airport with one, it will be confinscated.
Street vendors are decidely less aggresive than most Caribbean nations. A simple "no thank you" is sufficient.
Some of the locals will offer gifts when you stop however don't be naive - they expect something in return, so either refuse the gift in the first place or be prepared to pay a dollar or 2 for the proffered "gift". These people are very poor and unemployment is high so tourists are often the sole means they have to make some money.
Driving can be fun, but you should be a confident driver as driving is on the left, the roadways can be narrow, steep and in rough condition. A 4x4 or similar high-clearance vehicle is necessary if you decide to venture into the mountains. There's only one main roadway so it is difficult to get lost, but should it happen the locals will help you find your way.
Sexual acts between men are illegal and carry a custodial sentence of up to 10 years, though it is not known how strictly this is enforced. Gay travellers should be safer here than in, for example, Jamaica. However caution is advised and public displays of affection may be met with hostility. There is no law which explicitly forbids lesbianism.
This island is a series of hills and mountains. The main west coast roadway is the most hair-raising series of winding hair pin turns you have ever seen, particularly between Castries and Soufriere. The east coast roadway is more direct but it still takes approximately 90 minutes to drive from the airport in Hewannora UVF to Castries and Gros Islet in the north. In preparation for the shuttle, people who are staying in the north and are prone to motion sickness, should bring Dramamine and take it immediately upon arrival at Hewannora Airport.
Tap water is safe to drink, however bottled water is widely available for those who desire it.