There are several ways to carry your landscape filters with you in the field. Singh-Ray includes a very nice pouch for each of their filters, both screw-on and grad filter. For round filters many use the folding filter wallet. These solutions easily fit in most bags and allow you to select the filter you need in a reasonably organized fashion. I have used these solutions but I have also found that they slow me down since it requires me to stop, open your bag, find the case, then pull out what I need. Of course this works but for me there is a better way to carry the 10 filters I use so I can get to them much faster. My solution in the field is to carry all my filters on my hip/belt so I can quickly and easily grab what I need without having to dig into my bag. Everything I need is literally at my fingertips inside two filter pouches.
For my grad-ND’s I use the Adorama Slinger to carry my filters. It is well padded, easily attaches to my belt using a Velcro strap, and can hold up to five filters up to 4” x 6” (Z-size). This works out well for me since I happen to own five grad-ND’s and I have a system so that every filter has its own place and they always go back in that place when finished. Starting from the outside in I place my 1-hard, 2-soft, 2-hard, 3-soft and 3-hard. This allows me to find what I need by position without the need to read the fine print or examine each filter. Each filter is placed in the pouch with the clear side up and I also use a folded pec-pad that I individually label, 1H, 2S, 2H, 3S and 3H, so I can grab each one without worry of getting my grubby fingerprints on any of them. This makes pulling out the appropriate filter extremely fast without fear of getting them dirty or grabbing the wrong one.
For my round screw-on filters I use the Tamrac filter case which also attaches to my belt via a Velcro strap. I own two of them, one that holds three filters and one that holds five. For major trips I always use the larger five-place case, which also has more room in each slot for thick filters. Inside that I have five filters and like my grad-ND filter pouch, each has its place so I can find what I need by its position. My five filters are my circular polarizer, 3-stop ND, UV protective filter (which I rarely use but always keep close in case of foul weather or children with sticky fingers), a Hitech 4x4 4-stop ND filter which I often hold over my CPL to get both polarization and long shutter speeds, and my thicker Canon 500D close-up filter/lens for when I need to get a close up and do not have my macro lens handy. I also keep a spare lens cap (sometimes attached to a step-up ring) in the case filling up all five slots.
When I step out of my car wearing these filter holders, one each hip, I sort of look like gunslinger from the old west --- a good example since they used theirs for a quick draw and this system is optimized for efficiency. I often get strange looks at first from other photographers --- what the heck is he wearing??? That look does not last long since it is often immediately followed by a look of, why didn’t I think of that!!! I find this system to work incredibly well. I have everything I need at my fingertips and without looking I know exactly where everything is. This is one of those things that makes life in the field just that much easier.