WHAT SIZE BACKPACK? -It doesn't make too much difference whether you're travelling in summer or winter. Perhaps you would choose a larger backpack for carrying bulkier winter clothing but remember the most important consideration is to choose a backpack that is right for you...your height, weight etc. If you can carry your backpack comfortably, you'll have a great trip.

SECURITY - Get small padlocks for your bag or a complete wire security mesh so you can lock it to the bunkbed , this way noone can take anything from it

TRAVELLING IN SUMMER- This generally means travelling more lightly. Try the pack on for size - empty backpacks all feel very comfortable so ask the shop assistant to help you fill it with whatever is lying around the store, just to give you an idea of how heavy it might be and to see how comfortable the pack feels across your shoulders.
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SLEEPING BAGS- are a great investment but lets face it, in some hotter countries you just dont have need them. . And in some hostels in australia , new zealand and canada the are not allowed to be used beacause of the spreading of BED BUGS . yyuuccckkk...
I'd say 80 percent of hostels provide free sheets and linen or a duvee or doonna
And the rest might charge you a dollar or 2 to rent theres,
Most tour companies provide the option of hiring a sleeping bag if your in colder countries and you have to use one for a week or two . just check the climate of the countries you go to .In the summer months you will find that a sleeping bag is too warm for this climate however it can still come in handy - sleep on top of it for extra comfort. go down to the beach with the sleeping bag and someone special . joking...
GENERAL RULE -You probably dont need to pack a sleeping bag

TRAVELLING IN WINTER- You'll need a slightly larger pack for winter travel - winter clothes are larger and bulkier, you need extra socks , however, if you pack sensibly you should be able to layer your clothing for extra warmth and swap the layers around for variety. The golden rule....one jacket only!! you dont perspire as much in winter so clothes dont get as smelly , but just make sure things dont get damp in damp in your pack. , some packs come with a waterproof jacket that un folds aroung the pack , or you could purchase 1 for $10 bucks

MAKE A CHECK LIST - Dont you hate it when you forget your toothbrush , or worse you left your passport behind , most things you can replace cheaply enough on your arrival . But some things you cant so easily! Passport , travellers cheques , plane/train tickets, wallet, cash and credit cards.

Craig M