Great question! I'm gonna reference my answers based on "Cribb, Paul J, Hayes, Alan, "Effects of Supplement-Timing and Resistance Exercise on Skeletal Muscle Hypertrophy." Medicine and Science in Sports and Exercise, 38(11). Pp. 1918-1925. ISSN 0195-9131, 1530-0315." and "Tipton, et al, "Timing of amino-acid carbohydrate ingestion alters anabolic response of muscle to resistance exercise." American Journal of Physiology - Endocrinology and Metabolism, 1 August 2001, Vol, 281 no.2, E197-E206 DOI:"
Now, before your workout, you want to consume something that's going to slowly release you solid amounts of energy over a long period of time. In other words, you want a food that releases your blood sugar minimally so you don't spike your insulin as much and do all of the nutrient transport work at once. Foods that accomplish this task are complex-carbs or as you mentioned low-glycemic carbs, which include oatmeal, brown rice, most veggies and some fruits. Also, it is not wise to think ONLY in terms of carbs for pre-training as protein is equally as important but luckily not anywehere near as complicated. Simply consume some protein with this carb-meal, (20-50g is ideal). By ingesting protein before and during a workout, you spare muscle protein, negate protein degradation, and set the muscle up for regeneration and remodeling. Loading protein and carbs before and again during the workout also leads to fat oxidation that continues long after the workout.
To understand what you must consume "during" your workout , i.e in that little interval you have, you must understand what's happening in your body. First, If intra-workout insulin is low, glucagon robs muscles of amino acids so it can convert them to glucose. Low insulin makes it possible for catabolic hormones to "steal" your energy and ultimately muscles. Muscles need carbs to do work, but they also need protein. During a workout, amino acid requirements go up 500%.
Based on this, and a few other studies that I've looked at over the years, it is best to consume a BCAA (branched chain amino acids) supplement. There are tons of these available, and I'll let you look online to find one that suits you economically.
Furthermore, if you read the above carefully, I also mentioned a bunch of negative things happening while your insulin is low during the workout. Well, what raises insulin then? The complete opposite of complex carbs...simple carbs (or high-glycemic foods). A VERY VERY good high GI carbohydrate that also has a bunch of other benefits are bananas! So eat a banana or two during this interval with some BCAAs and you are golden. You can also eat carrots, melons ,pineapple, quick white bread sandwich with protein in it (ham, turkey whatever).
You didn't say you wanted post workout nutrition help but if you comment that you would like to then just let me know :)
EDIT: I completely forgot another supplement that raises your insulin that you could consume during your workout, and this might surprise some people, but it is just plain old whey protein. Whey has been shown to spike insulin in hundreds of studies (primarily caused by leucine).