2 bikinis + 1 dress (or the equivalent) = pretty much all you really need! 
However, here is a check-list of other basic items to consider:

Seychelles packing check-list

1. Any medication you use (carry by hand)
2. Sunscreen (reef friendly)
3. Sunglasses & Hat
4. Summer Light clothing 
5. A pair of flip flops. Trainers if you plan to do nature walks or sports.
6. A Beach bag. Back pack for nature trails/hiking & small water proof bag for boat trips.
7. Snorkelling equipment (mask & tube, flippers optional)
8. UV bathing shirt (if you are fair-skinned) & reef/water shoes optional
9. Bio insect repellent & bite cream (can get here)
10. Body wash, shampoo, conditioner
11. Charger 
12. Reusable water bottle
13. Camera if your phone is not sufficient (and power bank if needed), binoculars if you want to bird watch
14. Light beach towel or sarong
15. Torch/headlight if you are staying on La Digue
Warm clothes for return flight

Documents (check validity)
Passport
Driving Licence
Health & travel insurance
Some Cash, Euro and USD most widely used (USD after 2009 issue, one bank accepts older notes for now but charges an additional 1% commission)
Credit cards (It costs more to draw from ATM cash machine with lower exchange rates, our guests tell us. If your credit card does not work, you will need to put down a cash deposit to hire a car).
Hotel voucher (if you are booking via a travel agent)
Weddings have additional document requirements.

Entry to Seychelles
Click link above for the Seychelles Electronic Border System requirements for entry to Seychelles which is mandatory. Applications can only be made up to 30 days prior to your arrival date in Seychelles. 
Seychelles is a visa-free country, however, a visitor's permit will be obtained upon arrival if you meet certain criteria click here.

Duty Free allowance per person (personal consumption)
200ml of Perfume and Eau de Toilette;
2 litres of alcoholic beverages containing less than or equal to 16% alcohol (such as beer, wine and sparkling wine);
2 litres of alcoholic beverages containing more than 16% alcohol (such as whisky, rum, gin and fermented or distilled liqueur);
250 grams of tobacco product or 200 cigarettes. Tobacco product includes but is not limited to cigars, cheroots, smoking & chewing tobacco and snuff.

There are some items that are prohibited or restricted to bring in, here is the list. This includes plant and plant products, wood, meat, vegetables and fruit. NO BALLOONS, balloons are banned in Seychelles.

Please do not hesitate to ask if you have any questions.

We look forward to your stay with us!