When winter's through, the lightening days bring the season of the lightened rucksack - gradually the need to be armed to the teeth with crampons, ice axes, snow shovels and spare woolly hats to decorate your snowman are giving way to the warmer days when the heaviest item you're carrying might be a bottle of chilled wine to enjoy during a lazy hour or two by a felltop tarn in the sun.

Less weight means smaller rucksack capacity. You'll probably only be lugging 5kg of gear, so we're talking 20 to 30 litres sacks, perhaps 35 if you insist on hauling bulky waterproofs everywhere. A simple rucksack, barely more than a bag with shoulder straps, will easily carry such small loads.

Trouble is, these days such sacks are hard to find. Today's bells and whistle models look like miniature backpacking sacks, with frames, padded hipbelts and a plethora of webbing and buckles. These extra features add weight and complexity and don't make carrying small loads any more comfortable. Indeed, unless they fit properly they are less comfortable, especially those with curved frames and an air gap between your back and the sack, a design which transfers the weight to the base of the pack where pressure points can occur at either side of the small of the back. If they're a precise fit there's no problem, but as they usually only come in one size a precise fit is rare. The air gap is designed to keep your back dry but while it might disperse a little dampness it won't stop you sweating - you'll still have a wet back when you're working hard. The wind can whip through these gaps too, upsetting balance.

Some modern design features are worth having. Padded backs are comfortable and make packing rucksacks easier. Rucksacks shaped to follow the curves of your back are comfortable and, more importantly, very stable as they move with you rather than against you. You'll get a sweatier back than with a sack that is held away from you but I'd rather have comfort and stability. Hipbelts or waist straps stop the pack bouncing when moving fast and increase the stability without the need for excessive strap tightening.

The variety of back systems means it's important to try on rucksacks loaded, to check they are comfortable; if you feel pressure points or rubbing try another model.

You're going out for the day - you don't need to carry much, so it doesn't matter if your packed lunch ends up in a carrier bag, right? Wrong. That might be the extent of your kit requirements for a half-hour stroll from the car park, but there's a bit more to it than that if you want to enjoy a full day out in wild country.

You need something with space enough, not just for sarnies and a bottle or flask of drink, but your waterproofs, a spare jumper, hat and gloves, as well as a survival bag if you're heading into wild country. That takes up a bit more space than a carrier bag, so your ideal daysack will probably be in the 20 to 30 litre range - 35 max.

Smaller daysacks will have a soft back, in other words, no frame or stiffening. As you get up to the 30 litre end, you'll see sacks either with alloy staves or rigid plastic inserts to keep the back stiff. The bit that makes contact with your back wants enough padding to give you a comfortable fit, and protect you from any hard lumps you might have packed in the sack. Better quality sacks will have back panels allowing a degree of ventilation, either by channels between separate pads, or by open cell foam covered with a breathable mesh fabric.

Contact fabrics
Ideally, the back of the ruksack and underside of the shoulder straps need to be covered with a fabric which is reasonably soft. You may not be going shirtless, but other outdoors clothing won't necessarily take kindly to abrasion.

Not absolutely essential at this capacity, but the means to compartmentalise some of your kit, particularly smaller items, is not a bad thing. The variations are enormous, but pockets may be on the sides, front or lid. Invariably zip fastened, small side pockets are most efficient with curved zipped openings which run in a vertical plane - in other words, opening a panel in the side of the pocket rather than a lid at the top.

Waist strap
Smaller daysacks may not be provided with a waist strap - but they're a lot more common now on the larger models. They contribute a great deal to stability, particularly if you're picking your way over rough ground, or doing something daft like running! Also useful for attaching small belt loop items like a camera or binoculars in a pouch.

Profile straps
These are the straps which hold the lid down, usually secured with quick release buckles. Handy also for holding down items you might not have room for in the main body of the sack, or something you want quick access to, like a waterproof jacket.
Common to all rucksacks without zip fastened main compartments.

 A lid with one or two straps and buckles - these days invariably using quick release fasteners - is the norm. Access from the top of the sack is what most walkers look for, because it's easy to stand the sack on its base and rummage around for your lunch box. The alternative is a daysack with zip fastened front panel opening, often popular as well for more general use - shopping, school, etc.