You can decide how exactly island will look. Island World uses .schematic files in McEdit/WorldEdit format. You can design own island and put schematic into schematics folder. Inside schematic you can put of course chest with items inside, or if you want more than one chest.
To setup spawn inside schematic put End portal block (id:120)
You can also put sign in schematic with first line [spawn], then sign facing will be used for teleporting to spawn.
Items in chest
When you update your server to new version there is possiblity that after island creation chest is empty - you need to update World Edit to latest version compatibile with your Craftbukkit/Spigot. You need to have CORRECT version of worldedit.
FOR EXAMPLE :
If you are using 1.6.4 bukkit you need to have WE for 1.6.4 and for 1.6.2 is not correct ! If you have bukkit 1.7 version, you need WE for 1.7 version, so any older version will be not correct !
When you creating island check console, if you will see msg "No compatible nms block class found" - it means that you have incorrect version of WorldEdit !
If you are using latest version from dev.bukkit and you still have no item in chest you probably need to try updated version (non-stable) from that www site : WorldEdit builds
For 1.8 spigot you need special version of WorldEdit dedicated to new spigot. Download it here.
If you have problems with finding correct version you should close your server, or just use options in config to fill chests. Check configuration page for more info.
Always try to find correct version of WorldEdit using DEFAULT SCHEMATIC since if you make own schematic using incorrect version of WE, chest was not saved correctly and is empty always - even if you install correct version of WE. So test always with default schematic!
If you have one world without multiverse your spawn point must be on negative coords outside island area.
Coordinates -100 -100 should be enough because 1st island will be generated at 0 0.
Problem with spawn
If visit is not working becaue 'problem with spawn' you need to rebuild spawn point. It needs to have 2 solid blocks under spawn point. Near spawnpoint you cannot have trapdoors, pistons, or lava.
To make chestshop working on islands you need to use 'allowed' list config. Just add sign id 68 to that list.